Pool Safety Regulations in Europe: Challenges Towards a Framework for Sustainable Seawater Utilization in Public Swimming Pools
by
, , , ,
Tatsiana Pobat
1
,
Georgia D. Mandilara
2, 
Federica Nigro Di Gregorio
3,
Federica Valeriani
1
,
Enrico Veschetti
3,
Emanuele Ferretti
3,
Athena Mavridou
4 and
Vincenzo Romano Spica
1,*
1
Public Health Unit, Epidemiology and Biotechnology Laboratory, Department of Movement, Human and Health Sciences, University of Rome “Foro Italico”, 00135 Rome, Italy
2
Department of Public Health Policy, School of Public Health, University of West Attica, 11521 Athens, Greece
3
National Center for Water Safety, Italian National Institute of Health, 00161 Rome, Italy
4
Department of Biomedical Sciences, University of West Attica, 12210 Aigaleo, Greece
*
Author to whom correspondence should be addressed.
Water 2025, 17(17), 2544; https://doi.org/10.3390/w17172544
Submission received: 1 July 2025
/
Revised: 5 August 2025
/
Accepted: 23 August 2025
/
Published: 27 August 2025
(This article belongs to the Special Issue Advances in Swimming Pool Hygiene Safety and Spa Research)
Abstract
The use of seawater in public swimming pools could offer a more sustainable solution given the challenges posed by climate change and the growing scarcity of potable water across Europe. However, the swimming pool sector currently lacks a unified European legislative framework and faces significant fragmentation, particularly regarding the use of seawater. This scoping review applies a methodology to collect and analyze the international and national regulations of 23 coastal European countries relevant to swimming pool water safety. It provides an overview of existing European legislation on the use of seawater in public swimming pools and outlines the permitted disinfection methods. The review also highlights the highly variable and fragmented regulatory frameworks for microbiological and chemical water quality parameters, as well as the limits imposed on disinfection by-products (DBPs). Furthermore, it addresses the potential risks associated with seawater use in pools, with particular attention to the toxicity of DBPs that may form under such conditions. The findings underscore the urgent need for legislative updates in the pool sector and highlight the potential for developing specific European regulations. These would help harmonize practices across the sector and improve the management of both sustainability and public health in recreational aquatic environments.
1. Introduction
The scarcity of high-quality freshwater has become a persistent and structural challenge in many parts of the world, affecting both communities and industries. This issue arises from a combination of factors, including widespread water pollution and the intensifying effects of climate change, which have led to more frequent and prolonged droughts, particularly in southern Europe. For instance, according to a report by the Italian Institute for Environmental Protection and Research (ISPRA), in 2022, Italy experienced a historic 52% reduction in its annual water availability compared to the 1951–2022 average [1]. Drought has a significant impact on the availability and quality of water used for swimming pools, potentially disrupting the entire water supply chain. This issue is particularly critical for the tourism and hospitality sectors, where swimming pools are considered key assets [2]. In southern European regions most affected by water stress, such as Spain, France, Portugal, Italy, and Greece, local authorities have been forced in recent years to implement restrictions on potable water use and temporary bans on filling swimming pools. These measures highlight the vulnerability of recreational water infrastructure to persistent water stress and emphasize the urgent need for sustainable water management strategies.
To address and mitigate these challenges, the European Union (EU) adopted the Water Framework Directive (2000/60/EC) [3], which, together with its “daughter directives”, provides a strategic basis for the sustainable management and protection of groundwater resources. In parallel, EU Member States have launched a series of initiatives under the European Green Deal aimed at reducing pollution and restoring a healthier balance between human activities and natural ecosystems with the goal of making Europe climate-neutral by 2050. Furthermore, the European Commission is developing a new water Resilience Strategy [4]. One of the key responses to the water crisis involves exploring innovative and sustainable alternatives to the use of potable water. Within this context, the swimming pool sector, which provides millions of people with opportunities for sport, leisure, rehabilitation, and wellness—is also being called upon to adopt more sustainable water management practices. Population growth, changing lifestyles, and the rising popularity of swimming have led to the expansion of a wide variety of facilities, such as sports and recreational pools, water parks, children’s pools, and whirlpools, located in both public and private settings, such as hotels, hospitals, schools, and spas [5]. This expansion has significantly increased water demand, making the adoption of water-saving strategies essential.
Among the proposed solutions to reduce potable water consumption in pools is the use of seawater for pool filling. Although the use of seawater is not entirely new—having been practiced in thalassotherapy centers since the late 19th century—today, seawater pools treated with disinfectants analogous to those used in freshwater facilities are already present in wellness and spa centers across several European countries. This sector is expanding rapidly [6], and the use of seawater is increasingly being reconsidered as a practical response to the water emergency, potentially paving the way for its broader adoption in various categories of public swimming pools. A notable example is Greece, which in 2025 authorized the use of seawater in hotel swimming pools [7]. This emerging trend necessitates a thorough assessment of the current regulatory framework on swimming pool water quality, which remains fragmented, along with a careful analysis of the potential public health and environmental risks associated with the systematic use of seawater in swimming pools.
Swimming pool water quality has attracted increasing scientific attention in recent years, as reflected in a growing number of global studies. This interest is driven by the widely recognized health benefits of swimming, alongside the recognition that frequent or intensive pool use can pose considerable public health risks [6,8,9]. This risk is primarily associated with the presence of microorganisms, including pathogens, in pool water, necessitating disinfection to prevent the spread of infectious diseases. However, disinfection leads to the formation of toxic disinfection by-products (DBPs), which result from the reactions between organic and inorganic compounds in pool water and disinfectants. Currently, more than 100 DBPs have been detected in both pool water and air [9]. These compounds span multiple chemical classes, and their type and concentration are influenced by several factors, including the source water used to fill the pool, the type and dosage of disinfectants, pH, temperature, swimmer load, and ventilation [10,11,12]. Chronic exposure to DBPs has been associated with a range of health issues, including skin and eye irritation, asthma, bladder and colon cancer, adverse reproductive and neurotoxic effects, and liver and kidney damage [8,9,10,11,12,13,14,15]. The toxic action of DBPs varies by compound and exposure route. Swimmers may be exposed to DBPs through five main routes: inhalation, dermal, ingestion, buccal, and aural [16], representing a broader spectrum of exposure pathways compared to drinking water. This necessitates careful assessment and management of the associated health risks.
While tap and freshwater are the most common pool filling sources, seawater and mixtures thereof are occasionally used as alternative options, as reported in several studies [6,8,9,10,11,12,13,14,15,17,18,19,20,21,22,23,24,25,26]. Despite the well-documented public health risks associated with swimming [16], which necessitate careful consideration and assessment to ensure users’ and workers’ safety, there are currently no binding international or EU regulation for swimming pools treatment, aside from the non-binding recommendations provided by the World Health Organization (WHO) [27]. Requirements in this sector are often defined by state or local authorities, or by guidelines issued by local associations or advisory bodies such as the Pool Water Treatment Advisory Group (PWTAG). Although DBPs in swimming pools have been studied for decades, there remains a lack of standardized guidelines or limits, even for pools filled with potable water. For seawater pools, data on DBP occurrence and the related health risks are still scarce, and significantly more limited than for freshwater pools [6].
In view of all the above, it was necessary to create a comprehensive overview regarding the use of seawater in swimming pools. This is, to our knowledge, the first review of the regulatory frameworks on pool water quality in European coastal countries, with a specific focus on seawater use and its implications. This scoping review aims to provide a systematic analysis of the regulatory frameworks governing pool water quality across 23 European countries with access to the sea or ocean. The primary objective is to assess the extent to which national regulations permit or consider the use of seawater as an alternative to freshwater for filling pools, offering a comprehensive and practical overview for stakeholders in the recreational water sector. The review also investigates the disinfection methods permitted by national regulations, with particular attention being paid to the implications of these treatments when applied to seawater. Furthermore, it evaluates the existing microbiological and chemical water quality requirements, as well as the potential public health and environmental risks associated with the systematic use of seawater in swimming pools, with a particular focus on DBPs. By mapping regulatory trends, disinfection practices, and health risks, this review is intended to support policymakers, public health authorities, facility managers, and researchers in identifying gaps and highlighting directions for future research in the context of sustainable water use in recreational facilities.
2. Materials and Methods
This study is a scoping review [28] conducted to clarify the legislative framework regarding the potential use of seawater in public swimming pools within the European Union. The review specifically focuses on all 22 EU Member States with access to the sea or ocean, as this geographical condition is a prerequisite for the possible development of coastal pool infrastructures supplied with seawater. To broaden the scope of the investigation, an attempt was also made to include other European countries with sea access, such as those officially applying for EU membership. However, due to the unavailability of relevant legislative documents, either inaccessible or behind paywalls, only Albania was included as the 23rd country in the review.
Prior to initiating the review, a two-person research team was established. One researcher had a background in chemistry and environmental science, along with multidisciplinary expertise, including water quality. The second researcher had a background in hygiene and public health, with multidisciplinary expertise, including research methodology, literature search strategies, as well as extensive experience in conducting both scoping and systematic reviews.
The primary objective of this research was to collect and analyze existing regulations or guidelines concerning water quality and safety in swimming pools, with a specific focus on how they address the use of seawater. The review also aimed to examine the disinfection methods required by such regulations and to identify the physicochemical and microbiological quality indicators monitored in swimming pools across Europe to ensure hygiene and safety for both swimmers and staff. Furthermore, it investigated whether scientific evidence exists that would indicate a higher chemical risk, particularly in terms of disinfection by-product formation, in seawater pools compared to freshwater pools.
This review was conducted following the methodological framework proposed by the Joanna Briggs Institute (JBI) for scoping reviews and is reported in accordance with the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews) checklist (Supplementary Table S5).
The literature search was carried out between January and March 2025. To collect regulatory documents and technical guidelines, we consulted the official institutional websites of competent national and local authorities in Europe, recognized legislative portals authorized to publish regulatory texts, and the official websites of professional associations responsible for issuing sector-specific guidelines. To investigate the chemical risks associated with seawater swimming pools, particularly related to disinfection practices and DBP formation, PubMed and Scopus were selected as the primary databases due to their broad coverage of environmental and chemical sciences, consistent with the focus of our study. These databases were systematically searched for all works published up to March 2025 to retrieve the relevant scientific literature. The search strategy employed a combination of keywords, including “swimming pools”, “seawater”, “disinfection”, and “DBPs”. Additionally, we manually screened the reference lists of key research articles and reviews related to swimming pool water quality. Grey literature and regulatory reports were also included to capture the potentially relevant information not indexed in academic databases.
The inclusion criteria were as follows:
- Regulatory documents or scientific articles published in English or in the original language;
- Studies and regulatory texts addressing the quality and safety of water in public swimming pools, with specific attention to the use of seawater;
- Scientific articles and other literature providing data on physical-chemical and microbiological parameters, disinfection methods, or DBPs formation in seawater pools.
The selection process consisted of two phases: the initial screening of titles and abstracts, followed by full-text review to assess relevance to seawater-filled swimming pools. Disagreements between reviewers were resolved through discussion and consensus.
To construct the pie charts, which illustrate the distribution of different DBP classes in seawater- and freshwater-filled pools, DBP concentrations reported in the studies selected for this review were summarized in Supplementary Table S4. For each DBP class (e.g., HAAs or THMs), a mean concentration was calculated separately for seawater and freshwater pools, based on the values reported in the included articles. Where the total concentration of a DBP class was not explicitly provided by the original authors, it was estimated by summing the mean concentrations of the individual compounds belonging to that class. The line charts, which compare the cytotoxicity of DBP classes in relation to their abundance in the two pool types, were based on the same concentration data used for pie charts. Cytotoxicity was assessed using the average chronic cytotoxicity index for Chinese hamster ovary (CHO) cells, defined as the concentration causing a 50% reduction in cell viability (expressed in molar units as %C½ or LC50). LC50 values for individual DBPs were retrieved from the literature and included in Table S4. Based on these values, the median LC50 was calculated for each DBP class, and its inverse (1/LC50) was used for graphical representation.
3. Results
3.1. Overview of the European Legislative Framework on the Use of Seawater in Swimming Pools
In Europe, the public swimming pool sector is regulated by a vast range of technical standards. For instance, the EN 15288 standard provides relevant terminology and specifies design requirements to ensure safety in public swimming pools in its Part I [29]. Part II of this standard outlines the safety requirements for public swimming pool operation and offers guidance on risk assessment [30]. Additional standards define safety requirements for pool equipment and set rules for the use of chemical products in water treatment, including disinfection, filtration, and sampling [5,17]. Separate standards also exist that specifically address the domestic swimming pool sector.
However, technical standards are qualified recommendations rather than mandatory regulations that must be adhered to. Their application is voluntary, though universally beneficial. Currently, there are no harmonized European regulations or community guidelines concerning parameters related to the quality and safety of water and air in swimming pools. Legislation in this area is not uniform and varies from country to country. Local authorities have adopted diverse approaches based on their sensitivity to this aspect of public health. Moreover, most current regulations in Europe focus primarily on ensuring adequate water quality, while air quality in swimming pools remains relatively overlooked. In most cases, no mandatory chemical parameters are specified for air monitoring. When present, such parameters generally apply only to indoor pools and are typically limited to trichloramine—and occasionally ozone—being enforced in a few countries, including The Netherlands, Belgium, and Sweden, as detailed in Supplementary Tables S3 and S4.
According to the definition provided by the EN 15288 standard [29], a swimming pool is described as a “facility, with one or more water areas, intended for swimming, leisure or other water based physical activities”. Swimming pools are classified based on the type of facility as either indoor or outdoor. Furthermore, they are categorized according to the type of users, necessitating a distinct regulatory approach, generally falling into the following classifications:
- Public pools, which include both public and private facilities intended for collective use (e.g., municipal pools, water parks, hotel pools, therapeutic pools, pools in educational institutions, and so forth);
- Private pools, which refer to domestic pools used within a family context.
Inconsistencies arise even within the classification of swimming pools, for example, in the Flanders region of Belgium [31] and in Finland [32], certain hotel facilities are not classified as public pools. This discrepancy may lead to negative health outcomes for users or result in legal disputes, as regulations generally establish more stringent criteria for water quality parameters and health surveillance protocols for public pools, while private pools are often exempt from such regulations.
Swimming pools may be filled with freshwater, seawater, or thermal water [8]. There is no specific legislation governing pools filled with seawater; however, in several countries, including France, Poland, Germany, Slovenia, Croatia, Lithuania, Latvia, Romania, Denmark, and Malta, the common regulations or recommendations applicable to public swimming pools explicitly permit the use of seawater. These regulations often specify certain qualitative parameters that either do not need to be monitored or, conversely, must be monitored when seawater is used.
It is important to note that European legislation generally distinguishes swimming pools from other categories, such as “bathing areas”, which are defined, for example, by the French “Public Health Code” [33], Article L. 1332-2, as “any part of surface water where a large number of people are expected to bathe and where the competent authority has not permanently prohibited bathing”. Another category is that of “thermal pools”, as defined by Article D. 1332-1 as those “supplied by natural mineral water and used for therapeutic purposes in a spa facility”. These categories are considered three distinct types of facilities and are often subject to separate regulatory requirements.
Article D. 1332-4 of the “Public Health Code” (PHC) [33] stipulates that swimming pools are supplied with water sourced from the public distribution network or taken from the natural environment. The use of the latter is subject to authorization by the competent authorities. Furthermore, the “Decree of 26 May 2021 on swimming pool water quality standards and reference values, pursuant to Article D. 1332-2 of the Public Health Code” [34] explicitly states that certain parameter limits, such as those for bromine content, apply solely to pools filled with seawater. Inversely, the limits for the Legionella pneumophila content do not apply in the case of whirlpools supplied with seawater. In addition to the above-mentioned legislation, the “Order of 26 May 2021 on the use of non-potable water sources for supplying swimming pools, pursuant to articles D. 1332-4 and D. 1332-10 of the Public Health Code” [35] is in force. This rule outlines the quality parameters that such water must meet prior to its use.
In Poland, the “Disposal of the Minister of Health of 9 November 2015 on water quality requirements for swimming pools” [36], prescribes that water in swimming pools should meet the microbiological and physicochemical requirements specified in its Annexes 1 and 2, which explicitly apply to waters: “(a) fresh, i.e., surface or underground waters that meets the requirements of the drinking water regulations; (b) salty, including sea and brine containing from 5 g/L to 15 g/L of minerals; (c) thermal, i.e., underground waters, which at the outlet from the intake have a temperature of not less than 20 °C (excluding water from the drainage of mining excavations)”.
In Germany, the safety of swimming pool waters is regulated by the “Infection Protection Act” (IfSG), specifically under Section 7, § 37 [37], and the technical rules outlined in the DIN 19643 series. The standard DIN 19643-1 “Treatment of water for swimming pools and baths—Part 1: General requirements” [38] applies to the swimming pool water, including seawater, mineral water, medicinal water, brine, and thermal water. It does not apply to the water in facilities using biologically treated water.
In Slovenia, the “Rules on minimum hygiene requirements that must be met by swimming pools and bathing water in pools” [39] require that bathing water in pools meet the hygiene requirements set out in Annex 1. The Annex contains tables specifying quality parameters, some of which are regulated differently, depending on whether the pool water is freshwater or seawater. The Rules divide pools into biological and conventional categories and apply to both, separately regulating their microbiological and chemical parameters.
In Croatia, the Ministry of Health “Rules on sanitary, technical and hygienic conditions of swimming pools and on the health safety of swimming pool waters. No. 1186” [40] is currently in effect. This regulation shares many similarities with the Slovenian one. It also categorizes swimming pools into conventional and biological types, establishing separate parameters for the quality of their waters. Furthermore, it specifies in Table 1 of Annex 1 the distinctions in certain parameters that must be adhered to when using freshwater or seawater for conventional swimming pools.
The Lithuanian Hygiene Norm HN 109:2016 “Public Health Safety requirements for swimming pools” [41], covering all types of swimming pools, explicitly stipulates that mineral and seawater may be utilized for the provision of pool services. However, it must comply with the requirements set forth in the Hygiene Norm HN 127:2010 “Mineral and seawater for external use. Health safety requirements” [42] prior to its use.
The Latvian Regulation No. 470 “Hygiene requirements for pool and sauna services” [43] also addresses the possibility of using seawater in pools. It stipulates that “If the pool is supplied with seawater or mineral water, its quality must comply with the microbiological quality indicators specified in Annex 2 of this regulation”.
Regarding Romania, “Order No. 994 of 9 August 2018, amending and supplementing the Public Hygiene and Health Norms No. 119/2014 on the population’s living environment” [44] specifically addresses public swimming pools and explicitly states in Article 102 that “Swimming pools/tubs may be filled with potable water or seawater. If the filling water is sourced locally from means other than the public potable water distribution network, it must comply with the legal provisions applicable to this matter”.
In Spain, the matter of water quality in swimming pools is regulated by the “Royal Decree 742/2013 of 27 September, establishing the technical and health criteria for swimming pools” [45], which applies to public and private swimming pools, except for natural swimming pools and thermal or mineral-medicinal baths. This Decree does not explicitly address the issue of the types of water permitted for filling swimming pools. However, it mandates that the competent authorities submit annual reports to the Ministry of Health, Social Services and Equality, containing periodic basic information related to public swimming pools, as specified in Annex IV. This includes the details regarding the source of the water supply, which, according to the text, may originate from (a) the public network, (b) a non-public network, or (c) seawater.
In Portugal, the standard NP 4542:2017 “Swimming pools. Quality and treatment requirements of water used in the pools” [46] and Directive CNQ No. 23/93 “Quality of public swimming pools” [47], both applicable to public swimming pools with the exceptions of thermal and therapeutic pools, stipulate that the water supply must come from a public water network. The use of alternative sources requires authorization from the competent authorities. The standard refers only to salt water in Table 1, which indicates that the chlorite measuring method is not applicable in the case of salt water. Additionally, Annex A specifies that the compensation tank must be designed and sized to receive new water, whether freshwater or seawater. At the same time, the Circular-Normative No. 14/DA “Health surveillance program for swimming pools” [48], separately regulates the physicochemical parameters to be controlled in freshwater pools and those in seawater pools.
In Sweden, emphasis is placed on self-management and self-inspection by swimming pool operators. The Public Health Agency, in its “Guidance on swimming pools No. 23048 of 5 February 2021” [49], alongside the “General Advice on swimming pools HSLF-FS 2021:11” [50], provides authorities with tools for supervision in accordance with the Environmental Code. The Guidance addresses various issues, including microbiological and chemical hazards associated with swimming pools, as well as examples of what may be included in the operator’s self-inspection and what can be monitored during supervision. These documents do not directly refer to the use of seawater in swimming pools, but they do state that some water quality control methods are not suitable when using saltwater. For example, the Guidance states that, when monitoring the conductivity and chloride content, “these methods do not make sense to use in pools with saltwater”.
In Finland, the “Instructions for the application of the swimming pool water regulation: Swimming pool water quality and monitoring. 2/2017” [32] are enforced by Valvira, the National Authority for Welfare and Health. These guidelines, based on Health Protection Act No. 763/1994 [51] and on the Ministry of Social Affairs and Health Decree No. 315/2002 “On the quality requirements and monitoring studies of pool water in swimming pools and spas” [52], and applicable to swimming pools, water parks, and spas, do not explicitly address the potential use of seawater. There is only one reference within the text that mentions it: “If the water used in the pools contains bromine (i.e., municipal water derived from seawater), it may also be necessary to determine brominated trihalomethanes”.
Danish regulations, including the “Guidance on controlling swimming pools. VEJ No. 9605 of 14 July 2020” [53] and the “Executive Order on swimming pool facilities and their water quality. BEK No. 918 of 27 June 2016” [54], specify that public swimming facilities (i.e., swimming pools and hot water baths, including spas, water parks, recreational pools, and similar facilities) may utilize surface waters sourced from the sea, rivers, lakes, or fjords. These regulations establish microbiological quality parameter requirements that differ from those applicable to pools using potable water.
The relevant Norwegian legislation is the “Regulation of 13 June 1996, relating to bathing facilities, swimming pools and saunas, etc.” [55] and pertains to all public bathing facilities, including swimming pools, saunas, and hot tubs. Regarding the swimming pool water, it stipulates that “the water in swimming pools must be hygienically satisfactory”’; however, it does not contain specific provisions concerning the quality of filling water or the potential use of seawater. Overall, this regulation requires updates and enhancements, as it mandates the monitoring of only a limited number of chemical and microbiological parameters related to water quality.
In The Netherlands, stringent regulations on water quality in swimming pools have been integrated into the “Environmental Activities Decision” (Bal) [56]. This transition allows for more targeted regulations and, together with the “Environmental Act” [57], gives operators more flexibility in meeting requirements, while imposing greater responsibility on them to develop risk assessments and safety and hygiene management plans. Chapter 15 “Providing the opportunity for swimming or bathing in a water pool” of the Bal defines the necessary criteria for both water and air quality in a swimming pool; however, it does not address the use of saline or seawater for pool filling. Nonetheless, it specifies some alternative quality criteria, if the salt content in the pool exceeds 14 g/L.
In Belgium, there is no unified national legislation governing the quality of water in public swimming pools, as it varies by region. In Wallonia, the “Government Order of 13 June 2013, determining full conditions for indoor and outdoor swimming pools used for a purpose other than purely private within the family circle” [58] is in force. Regarding the filling water, the Order does not directly mention seawater but indicates in Art.13 that “when the swimming pool filling water and supplementary water are not tap water, they meet the standards set for tap water”. In the Brussels-Capital Region, the “Government Order of 16 February 2023 setting operating conditions for swimming pools and other baths” [59] is in force. Its Article 3 stipulates that public swimming pools may be supplied with water not sourced from the potable water distribution network, provided that the relevant environmental permit explicitly authorizes this. In such cases, it must be demonstrated that the filling water does not pose a significant risk to the health of bathers or to the operation of the facilities. Meanwhile, in Flanders, compliance with Title II of the “Decree of the Flemish Government of 1 June 1995 containing general and sectoral provisions regarding environmental hygiene” (VLAREM II) [31] is required. Its Article 5.32.8.1.1, in addition to regulating water and air quality in conventional swimming pools, hot whirlpools, and therapy pools, also addresses natural swimming pools. This regulation does not explicitly mention the use of seawater; however, in the section pertaining to water quality parameters, it specifies that certain parameters “are not applied when using salt water (>2000 mg Cl/L) or when using salt electrolysis”.
In Italy, the “Agreement of 16 January 2003, concerning the health and hygiene requirements for the construction, maintenance and supervision of swimming pools” [60] is currently in force. This Agreement applies to all types of public swimming pools, except for thermal pools and those intended for rehabilitation and therapeutic use. Clause 3.3 of the Agreement explicitly states that swimming pools may be supplied with (a) freshwater (either surface or groundwater); (b) seawater; and (c) thermal water. It also provides that facilities using seawater and thermal water shall be subject to specific provisions established at the regional level. In the wake of this Agreement, an interregional technical framework titled “Interregional Regulation on swimming pools” [61] was approved on 22 June 2004 to support the harmonization of regional legislation.
However, despite the formal adoption of this Agreement by all Italian regions, only a subset has subsequently issued implementing regional regulations. Among the regions that have transposed the 2003 State-Regions Agreement into binding regional provisions, only a few, including the Emilia-Romagna [62], Liguria [63], Marche [64], and Tuscany [65], have addressed in detail specific hygiene and public health aspects related to the construction, operation, and supervision of recreational swimming pools, explicitly mentioning the use of seawater. Additionally, during the COVID-19 pandemic, the “Guidelines for the reopening of economic and productive activities” were issued by the Conference of Regions and Autonomous Provinces on 11 June 2020 [66]. These Guidelines included provisions for the treatments and disinfection of swimming pools supplied with seawater. However, none of the aforementioned documents specify the quality parameters that must be met for pools using seawater. Within this fragmented legislative framework, the need for comprehensive regulation that clearly defines this domain is evident.
In Albania, the Regulation “Hygienic and sanitary requirements for swimming pools. Act No. 835 of 30 Novembre 2011” [67] is similar to the Italian regulation and applies to public swimming pools, excluding those designated for therapeutic, curative, and thermal purposes. Notably, the regulation does not address the potential use of seawater for filling swimming pools; however, it mandates that the supplied water must comply with all potable water standards.
In Greece, the quality of water in public swimming pools is regulated by Sanitary Order Γ1/443/1973 “On swimming pools with instructions for their construction and operation” [68]. This Order was amended in 1976 and 2006 and is supplemented by a series of subsequent explanatory instructions on the subject. One such document, specifically the Circular ΔΥΓ2/99932/06/2007 “Instructions-clarifications for the implementation of the Health Provisions for the operation of swimming pools” [69], clarifies that the use of seawater to fill the pool does not contradict the provisions of the aforementioned Order, provided that the physical, chemical, and microbiological characteristics of the pool water comply with the specifications outlined in Article 15 of the Order. Within the legislative framework governing the concession of rights to use the foreshore, beach, bank, riparian zone, aquatic environment, seabed, and subsoil, a new provision was introduced this year through Law 5170/2025, Article 14 [7]. This amendment enables the execution of works for the installation of pipelines for the abstraction and discharge of seawater intended for use in swimming pools of legally operated hotel facilities. However, specific criteria on the quality standards of seawater-filled swimming pools have not yet been established.
In Bulgaria, the only existing regulatory act pertaining to the quality of water in public swimming pools appears to be “Instruction No. 34 on the hygiene of sports facilities and equipment” [70], issued by the Ministry of Health. This document does not mention the possibility of using seawater, nor does it generally delineate the sources of water supply. Article 33 specifies only that, when selecting a water source for the pool, quality control must be conducted in accordance with the provisions outlined in Article 18.
The Estonian Regulation No. 80, titled “Health protection requirements for swimming pools, pools and aquatic centres” [71], explicitly excludes mineral water and hydrotherapy pools from its scope. Furthermore, it does not address the potential use of seawater for pool replenishment, stating only that the water utilized in pools must comply with the standards established for drinking water.
In Malta, the “Swimming Pools Regulations, 2005, L.N. 129” [72] adopted under the Public Health Act No. XIII of 2003, is applicable to all types of public swimming pools, including thermal and therapeutic pools. These regulations do not specify the type of water that may be used to fill the pool but stipulate that the pool must be supplied with controlled water. Concurrently, the “Subsidiary Legislation 545.07 on control of swimming pools regulations” [73] is in effect, which in paragraph 6(2) states that “A pool located within a distance of one hundred meters from the sea, may be filled or replenished with seawater, if the requirements of paragraph 9 are observed”. Specifically, paragraph 9 dictates “Seawater, or any substance derived therefrom, shall not be emptied from any pool or discharged therefrom except via impermeable pipes leading directly to the sea”.
In Cyprus, public health regulation concerning swimming pools is governed by the “Public Swimming Pools Laws of 1992 and 1996” [74] (55(I)/1992 and 105(I)/1996). Water quality standards are delineated by “The Public Swimming Pools Regulations of 1996” (KDP 368/96) [75]. This regulation, which has long been recognized as needing updates, does not explicitly address the use of seawater for filling swimming pools. It contains only two somewhat relevant statements regarding this issue: “The competent Health Authority may, at its discretion, also permit the use of brackish water solely for the requirements of tanks and sanitary facilities” and “in the event of water renewal from a safe, non-chlorinated natural source, there must be a ratio of at least 2.000 litres of water per bather”.
A graphical summary of the legislative situation regarding seawater use in swimming pools across 23 European coastal countries is presented in Figure 1, while an overview is provided in Table 1. More detailed information on the 63 regulatory documents analyzed is Available in Table S1 of the Supplementary Materials.
Table 1.
Overview of national regulatory frameworks in European coastal countries concerning the use of seawater in public swimming pools.
Table 1.
Overview of national regulatory frameworks in European coastal countries concerning the use of seawater in public swimming pools.
| Country | Regulation | Scope of Application | Permitted Type of Filling Water | Ref. |
|---|---|---|---|---|
| France |
| Applies to public/collective swimming pools. Does not apply, except for disinfection provisions, to thermal SPs supplied by natural mineral water used for therapeutic purposes in thermal facilities. | Water from a public distribution network or from water taken from the natural environment, seawater included, after authorization. | [33] |
| [34] | |||
| [35] | |||
| [76] | |||
| [77] | |||
| Germany |
| Applies to public/commercial baths and non-private use SPs facilities. Does not apply to private baths; systems with biological treatment, water playgrounds, floating systems/pools; discontinuous water treatments. | [37] | |
| Water, including seawater, mineral, medicinal, artificially produced brine and thermal water. | [38] | ||
| [78] | |||
| [79] | |||
| [80] | |||
| [81] | |||
| Slovenia | Rules on minimum hygiene requirements that must be met by swimming pools and bathing water in pools. | Apply to bathing areas and water in conventional and biological SPs. Do not apply to natural bathing areas and SPs used by individuals or their family. | Freshwater and seawater. | [39] |
| Croatia | Rules on sanitary, technical, and hygienic conditions of swimming pools and on the health safety of swimming pool waters. No. 1186. | Do not apply to non-public SPs; SPs with medically indicated, therapeutic water (e.g., thermal), not disinfected with residual effect; saunas and hot tubs in which the water is used once; lagoons, flow pools, and seawater water slides. | Filling water from a public water supply system, seawater, or other type. | [40] |
| Poland |
| Does not apply to swimming pools filled with water with medicinal properties. | Freshwater, i.e., surface or groundwater, meeting the drinking water requirements; salty, i.e., brine and seawater, with 5–15 g/L of mineral content; thermal water with outlet temperature ≥ 20 °C. | [36] |
| [82] | |||
| Lithuania |
| Not specified. | Freshwater for pools must meet drinking water quality requirements before use. Mineral and seawater used to supply SPs must meet HN 127:2010 requirements before use. | [41] |
| [42] | |||
| Latvia | Regulation No. 470 “Hygiene requirements for pool and sauna services”. | Pools or saunas, including those in educational, social care, healthcare institutions, sports, entertainment or recreation facilities, and hotels. | Potable water with the mandatory safety requirements for drinking water, sea or mineral water. | [43] |
| Romania |
| Public swimming pools. | Drinking or seawater. Filling water not coming from public drinking water network, must comply with legal provisions. | [44] |
| For freshwater. | [83] | ||
| For seawater. | [84] | ||
| Spain |
| Applies to public SPs. Single-family private SPs and SPs in homeowners’ associations, agrotourism’s, colleges, or similar establishments must comply with some provisions of this Decree. Does not apply to natural, thermal or mineral medicinal pools. | Contains a request to provide periodic reports to the Ministry of Health with basic information on sources of filling water in SPs, which may include public and non-public networks or seawater. | [45] |
| [85] | |||
| Portugal |
| Public swimming pools. | Water from a public water network. Alternative water sources use requires the authorizations. | [46] |
| Public/semipublic swimming pools. | [48] | ||
| Applies to public SPs and aquatic recreational facilities. Does not apply to therapeutic or thermal facilities, SPs used by families, or in condominiums with less than 20 units. | Mention seawater use. | [47] | |
| Finland |
| Apply to public SPs and spas. Do not apply to residential SPs, SPs in which the water is changed after each use, hotels, Jacuzzis self-filled by users, wading pools without continuous water treatment, portable SPs, and hot tubs rented by customers. | Nor specified. | [32] |
| [51] | |||
| Applies to public SPs; spas; water parks; recreation and rehabilitation facilities. | Mention filling water rich of bromine. | [52] | |
| Sweden |
| Applies to public SPs, i.e., pools and tubs for swimming, which can be part of pools such as indoor SPs, spas, and water parks, or be independent both outdoors and indoors. | Nor specified. | [49] |
| [50] | |||
| [86] | |||
| Denmark |
| Applies to public and hot water SPs, i.e., spas, water parks, recreational, therapy, and treatment pools and similar. Does not apply to private SPs, paddling pools where the water is discarded after a few hours, steam, thermal baths and similar. | Potable water and surface water (seawater included). | [54] |
| [53] | |||
| [87] | |||
| Norway |
| Covers all public SPs, bathing facilities and saunas. | Filling water must be hygienically satisfactory. | [55] |
| [88] | |||
| [89] | |||
| The Netherlands |
| Does not apply to household SPs, SPs installed for up to 24 consecutive hours, intended for human-animal contact, or installed on vessels not permanently moored. | Water that meets the quality requirements for drinking water. | [56] |
| [57] | |||
| Belgium Flanders | Title II of VLAREM. Government Decree of 1 June 1995 containing general and sectoral provisions regarding environmental hygiene. Art. 5.32.8.1. | Applies to permanent and natural SPs, hot tubs, plunge, splash, and therapy pools, open swimming areas, recreation zones. Does not apply to private and hotels SPs not open to the public, which must comply with the provisions on the water treatment and chemicals storage. | Freshwater or salt water. | [31] |
| Belgium Walloon | Government Order of 13 June 2013 determining full conditions for indoor and outdoor swimming pools used for a purpose other than purely private within the family circle. | Applies to indoor and outdoor SPs used non-privately within the family, when the surface area ≤100 m2 or the depth is ≤40 cm, with chlorine used for disinfection. | Drinking water from the distribution network. If the filling and supplementary water do not come from the network, it meets the tap water standards. | [58] |
| Belgium Brussels-Capital Region |
| Applies to SPs and other baths listed in Annex 1 of [83]: excluding domestic SPs with a pool area ≤200 m2, other bathing facilities, and SPs with a pool area over 200 m2. Does not apply to SPs and other baths with alternative water treatment other than chemical disinfection or biological treatment. | Drinking water from the distribution network. When supplied water is not coming from the drinking water distribution network, authorization or environmental permits are requested. | [59] |
| [90] | |||
| Italy |
| Applies to public/collective SPs for swimming, training, diving, underwater, recreational activities, for children, multipurpose use. Does not apply to SPs for rehabilitation, curative and thermal use. The systems supplied with thermal and seawater to be regulated by specific regional provisions. | Freshwater (surface or underground) that meets the requirements of potability. If the supply water does not come from a public aqueduct, it is necessary to verify its suitability for human consumption. | [60] |
| [61] | |||
| Mention seawater use. | [66] | ||
| [91] | |||
| Albania | Regulation “Hygienic and sanitary requirements for swimming pools”. No. 835. | Applies to public/collective SPs for competition, training, diving, underwater activities, recreational, multifunctional, and use by children, in hotel, tourist complexes/villages, colleges, schools, universities, gyms, beauty salons, and residence complexes with over 4 units. Does not apply to private SPs, residence complexes with up to 4 units, thermal and therapeutic SPs. | Potable water. If the water supply is not provided by the water supply company, the water must be tested seasonally for the parameters for assessing the suitability of drinking water. | [67] |
| Greece |
| Public swimming pools. | [68] | |
| Supplying SPs with seawater does not contradict the provisions if the water quality meets the parameters specified in Art.15 of [66]. | [69] | ||
| [7] | |||
| [92] | |||
| [93] | |||
| Bulgaria | Instruction No. 34 on hygiene of sports facilities and equipment. Amended on 2 March 1984, 8 March 2002. | Applies to the facilities where sports competitions and training are held. | Not specified. | [70] |
| Estonia | Health protection requirements for swimming pools, pools and aquatic centres. No. 80 of 15 March 2007. Amended on 10 December 2009, 19 August 2011. | Applies to SPs, pools and aquatic centres, in public and private legal entities providing services related to swimming and bathing, including schools and preschool institutions. Do not apply to natural mineral water and hydrotherapy SPs, natural cold-water pools, bathing facilities with flow-through surface water. | Water used in SPs must meet the requirements established for drinking water. | [71] |
| Malta |
| Applies to public or commercial SPs, including artificial basins, for recreational bathing, swimming, diving, or therapeutic use, located indoors or outdoors. Does not apply to non-public or non-commercial SPs. | Controlled water supply. | [72] |
| SPs located more than 100 m from the sea may be filled only with freshwater collected as surface run-off or from public supply network. SPs within 100 m of the sea may be filled by seawater, only if the pool water is discharged to the sea through waterproof pipes | [73] | ||
| Cyprus |
| Applies to SPs: pools used principally for competitions or for training or education of athletes; indoor SPs located within an enclosed covered area; public swimming pools. | Filling water should be microbiologically and chemically suitable. Authorities may allow the use of brackish water for tanks and sanitary facilities. Water renewal from a safe non-chlorinated natural source is allowed with at least 2000 L per bather. | [74] |
| [75] |
The regulatory heterogeneity observed across European countries regarding recreational water management and permissible water sources for swimming pools presents significant challenges for stakeholders, including operators, technology providers, public authorities, and facility users. Inconsistent or incomplete legal frameworks hinder the coordinated adoption of sustainable water strategies, particularly in areas affected by water scarcity. The lack of harmonized guidelines discourages investment in advanced management systems, as regulatory uncertainty leads operators to prioritize cost savings over innovation. This misalignment also limits the development of interoperable monitoring protocols and unified reporting platforms, which are crucial for protecting public health. Moreover, divergent national approaches impede cross-border initiatives for alternative or treated water reuse, undermining EU-wide goals for integrated and resilient water management [4].
3.2. Overview of Swimming Pool Disinfection Requirements in the European Legislative Framework
The need for pool water treatment arises from the risks of infection associated with swimming in contaminated waters. Many microorganisms present in pools originate from bathers, while others are naturally occurring in the environment. In outdoor pools, birds and other animals may introduce contaminants into the water. Microorganisms, such as bacteria, fungi, protozoa, and viruses, can proliferate rapidly in aquatic environments, particularly in crowded areas like swimming pools, thereby posing a significant risk of the transmission of infections or diseases to both swimmers and staff [27]. Additionally, bathers introduce substances such as sweat, urine, hair [11], personal care products [24], and other contaminants, further exacerbating water contamination. Contaminated water can also quickly emit unpleasant odors, reducing the overall swimming experience.
Consequently, it is essential that pool water undergoes appropriate treatment to remove debris and microorganisms through a combination of cleaning, filtration, flocculation, water replacement, ventilation, and disinfection processes [27]. The main methods of swimming pool water disinfection are as follows:
- Chlorine disinfection: In most public swimming pools, chlorine-containing reagents are employed for water disinfection, typically in the form of gaseous chlorine, sodium hypochlorite or calcium hypochlorite [49]. The disinfection mechanism is the same regardless of whether chlorine is introduced in water as gas or hypochlorite, or generated on-site via electrochlorination, whereby sodium chloride (NaCl) is electrochemically converted into chlorine gas—a particularly relevant approach for seawater pools. The addition of chlorine-based disinfectants to water initiates the reactions shown by Equations (1)–(3), leading to the formation of hypochlorous acid (HOCl), the primary disinfectant. HOCl is a highly effective bactericidal agent due to its high reactivity, enabling it to oxidize various inorganic and organic substances present in the water [9]:
Cl2 + H2O ⇋ HOCl + H+ + Cl−
NaOCl + H2O → HOCl + Na+ + OH−
Ca(OCl)2 + H2O → 2HOCl + Ca2+ + 2OH−
HOCl ⇋ OCl− + H+
In pool water, chlorine is present in the form of ClO− e HClO. Both species are responsible for the disinfectant effect and are collectively measured as “free chlorine” [9]. They exist in an equilibrium dependent on pH. As the pH value increases, the formation of HClO decreases. Since ClO− has a lower disinfectant capacity than hypochlorous acid, the disinfectant efficacy diminishes with the rising pH, unless the amount of free chlorine is simultaneously increased. The release of free chlorine also ensures a residual disinfectant effect, which is essential for maintaining antimicrobial activity in the pool, particularly in the presence of numerous bathers [49].
In addition to chlorine, other disinfectants and disinfection methods are sometimes employed in pool water treatment [27], some of which can be used in combination with chlorine, or more rarely bromine [15], or a combination thereof.
- Ozone (O3): Ozone is a powerful oxidizer, which makes it an effective disinfectant against bacteria and other microorganisms. It can also help eliminate certain contaminants and DBPs from the water. O3 disinfection occurs in the treatment tank and does not provide residual disinfection, making them an unsuitable standalone method. Moreover, O3 is toxic and must not be released into areas accessible to swimmers or staff [49]. Additionally, it can produce other DBPs such as aldehydes, nitrosamines, carboxylic acids, and, as is particularly relevant to seawaters pools, the known carcinogen bromate [15,27].
- Ultraviolet light (UV): It can induce oxidation and UV photolysis is often used as a disinfection method due to its efficacy against bacteria, protozoa, and most viruses. It can also break down combined chlorine compounds and photodegrade certain DBPs, with medium-pressure UV lamps being more effective than low-pressure lamps for this purpose [22]. However, UV provides no residual disinfection. Furthermore, its effectiveness can be significantly reduced by water turbidity [27,94], which is especially relevant for seawater pools, emphasizing the importance of water filtration. From a sustainability perspective, UV systems, especially those using medium-pressure lamps, may involve higher energy consumption and maintenance costs, compared to other disinfection technologies.
As both O3 and UV light lack residual disinfectant activity, they are primarily used as complementary treatments to chlorine or bromine [15], enhancing its disinfectant efficacy through the generation of reactive hydroxyl radicals and reducing overall chlorine demand. This integrated approach may result in lower genotoxicity and cytotoxicity in chlorinated pool water. However, reaction pathways may also promote the formation of alternative DBPs when UV treatment is followed by chlorination [22].
- Chlorine dioxide (ClO2): ClO2 is a highly oxidizing gas with superior antimicrobial efficacy compared to other chlorine-based compounds. Its mechanism of action is also different from traditional chlorination. Due to its instability, ClO2 is typically generated on-site by mixing chlorate or chlorite salts with an acid. Additionally, its high volatility and toxicity, especially in air, poses safety challenges for use in swimming facilities [49].
- Bromine-based disinfectants: Bromine gas is rarely used directly. Instead, the formation of HOBr and OBr−, which inactivate microorganisms [9], is achieved by using bromochlorodimethylhydantoin or by combining sodium bromide with an oxidant (typically chlorine or ozone), leading to the reactions described by Equations (5) and (6):
NaBr + HOCl → HOBr + Na+ + Cl−
HOBr ⇋ OBr − + H+
Although HOBr and OBr− act similarly to HOCl and OCl−, their disinfectant efficacy is generally lower than those of chlorine-based compounds. Moreover, bromine-based disinfection may lead to the formation of brominated DBPs, which are often more toxic than their chlorinated counterparts [13], limiting its suitability in bromide-rich water such as seawater.
- Hydrogen peroxide (H2O2): Hydrogen peroxide is a strong oxidizing agent occasionally used for the disinfection of pools. It has slower and less antimicrobial action compared to chlorine. In addition, prolonged exposure to even relatively low concentrations of H2O2 can cause skin and eye irritation due to its potent oxidizing nature [49].
- Electrochemically generated mixed oxidants (EGMOs): EGMOs represent an advanced form of electrochlorination, increasingly used for the on-site generation of mixed disinfectants from saline or seawater sources. The electrolysis of NaCl-rich water produces primarily free chlorine as per Equation (7), which subsequently reacts with water by Equation (1) to form the main disinfectant, HOCl [9].
2Cl− → Cl2 + 2e−
The process also generates minor oxidants such as O3 and H2O2, enhancing the overall disinfection efficacy. In seawater systems, the oxidation of naturally occurring bromide leads to HOBr formation, further improving the disinfection performance. EGMOs are thus advantageous in seawater pools, ensuring effective microbial control and reducing the reliance on chemicals. However, the formation of brominated DBPs requires careful monitoring when applying this technology to seawater systems [9].
Overall, chlorine-based disinfectants remain the most commonly used in pool water treatment [11,25], including chlorine [10,13,19], hypochlorites [6,12,17,19,20,26], chlorine dioxide, and chlorisocyanurates or their acids [10,13,18,21]. Less frequently, ozone [15], UV radiation [23], UV combined with chlorine-based disinfectant [22], chloramines, bromine/bromide and EGMOs [8,9] are also employed.
Similarly to the heterogeneous situation on general issues surrounding the use of seawater in swimming pools, European regulations are quite discordant on the methods to be applied for disinfection.
The French PHC, which permits the use of seawater in swimming pools upon obtaining authorization, stipulates in Article D. 1332-2 the necessity for the filtration, treatment, disinfection, renewal, and recycling of water in public swimming pools [33]. Decree No. 81-324 of 7 April 1981 [76], amended in 2021 [77], in Article 10.-I, mandates that the treatment of pool water must include at least one stage of filtration and disinfection. Furthermore, Article 5.-I authorizes the use of chlorinated products such as gaseous chlorine and bleach for disinfection, as well as compounds containing trichloroisocyanuric acid or sodium or potassium dichloroisocyanurate, or calcium hypochlorite as stabilizers.
The Belgian regulation of Brussels [59] stipulates that water treatment in public swimming pools must include at least pre-filtration, filtration, oxidation in combination with disinfection, pH regulation, and the addition of new water. Furthermore, it requires that chemically disinfected pool water be treated with chlorine, either alone or in combination with other chemical treatments (such as ozone) or physical treatments (such as UV). Similarly, the regulation of the Walloon region [58], which applies to pools that solely use chlorine for disinfection, mandates that the water treatment process includes pre-filtration, filtration, disinfection, and a freshwater supply system. It also requires that the water in each public pool be disinfected and prohibits the direct addition of chemical products into the pool. Additionally, it specifies the substances used for pH regulation. The VLAREM II regulation in Flanders [31] states that “unless otherwise indicated in the environmental permit for the operation of classified facilities, chlorine is the only permitted disinfectant and oxidant”. Contrary to the regulations of Brussels and Wallonia, it prohibits the use of chlorine gas and chlorine stabilizers.
The German IfSG [37] specifies in § 37(2): “In swimming pools or bathing areas, water treatment must include disinfection”, emphasizing the necessity of ensuring that there is no risk to human health during swimming activities. The methods employed for disinfection are regulated by the DIN 19643 series of the standard “Water treatment in swimming pools and basins”, which permits the use of seawater in pools and is divided into five parts. Parts 2 through 5 contain detailed and comprehensive regulations for various combinations of water treatment processes in swimming pools. Specifically, these parts address the following: the use of fixed-bed filters and pre-filters (Part 2) [78], ozonization (Part 3) [79], ultrafiltration (Part 4) [80], and the use of bromine as a disinfectant produced by the ozonation of bromide-rich water (Part 5) [81], which is particularly relevant for seawater rich in bromide.
The Polish regulation [36], which permits the use of seawater in swimming pools, does not explicitly specify the mandatory treatment or disinfection steps. It requires that the pool water, including the water supplied to the pool, meet the microbiological and physicochemical requirements outlined in Annexes 1 and 2 of the regulation. In this context, the water quality parameters specified in the annexes are accompanied by notes, such as “if disinfection with chlorine compounds is supplemented by UV radiation or ozone” or “determined in the case of water ozonation after filtration through absorption”.
The Slovenian rules [39] stipulate that, in the preparation of water for conventional swimming pools, at least residual disinfection and pH correction must be performed. Although an exhaustive list of disinfectants is not provided, the continuous and automatic measurement of free chlorine is required when chlorine is used as the disinfectant.
Similarly, the Croatian rules [40] stipulate that, during the preparation of water for conventional swimming pools, at least a disinfection process with a residual effect and pH regulation must be carried out. Regarding the substances used in pool water preparation, it is specified that the addition of substances other than those necessary for this process is prohibited. Furthermore, such substances and any impurities contained therein must not be present in the water at concentrations exceeding the established limits, and they must not pose a risk to human health.
The Lithuanian standard HN 109:2016 [41], which allows the use of seawater, stipulates that pool water must circulate, be filtered, coagulated, disinfected, and have its pH level regulated. Additionally, it specifies that biocidal agents, such as chlorine, bromine, and other compounds, must be employed for water disinfection in accordance with the provisions of Regulation (EU) No 528/2012 concerning making biocidal products Available on the market and their use possible [95]. The standard further indicates that UV light and ozone may be used as complementary agents to chlorine-based compounds for pool water disinfection, while only ozone is permitted as an adjunct to bromine-based compounds.
Latvian Regulation No. 470 [43], which also permits the use of seawater, generally stipulates that, in swimming pools equipped with a water purification system, purification and disinfection processes must be carried out in accordance with the manufacturer’s instructions for the pool equipment and in compliance with the operational standards for such equipment. Additionally, its Annex 1 provides information on the water quality parameters that must be monitored in a swimming pool, depending on the type of disinfectant employed: chlorine-based or bromine-based.
The Romanian Order [44] stipulates in Article 10 that both indoor and outdoor pools, as well as saltwater pools, must be equipped with water filtration and disinfection systems. Furthermore, Article 104 mandates that chemical products used as disinfectants for pool water must be approved by the National Biocidal Products Committee, in accordance with the relevant government regulation, which establishes the institutional framework and implements measures of Regulation (EU) No. 528/2012 [95].
Regarding Spain, Royal Decree 742/2013 [45] stipulates that recirculation water must be at least filtered and disinfected prior to being introduced into the pool. This requirement also applies to filling water that does not originate from the public distribution network, which may, by extension, include seawater, as indirectly mentioned in the text. Annex 1 of the decree specifies the water quality parameters, accompanied by annotations indicating the monitoring requirements based on the disinfectant used: “monitored when chlorine or chlorine derivatives are used as disinfectants”, “monitored when bromine is used as a disinfectant”, “monitored when trichloroisocyanuric acid derivatives are used”, and “measured when disinfectants other than chlorine or bromine and their derivatives are used”. The decree further establishes that only biocides classified as Type 2 Disinfectants pursuant to Royal Decree 1054/2002 may be used for swimming pool water treatment. Additionally, all other chemicals used in pool water treatment must comply with the requirements set forth in Regulation (EC) 1907/2006 (REACH) [96] and any other applicable specific regulations.
In Portugal, the CNQ Directive No. 23/93 [47] and Circular No. 14/DA [48], regarding treatment procedures, specify that, for pools authorized to use seawater or other high-dissolution-rate sources, filtration rates must be reduced by 30% or less, as indicated in Section 9.9 of the Directive [47]. Furthermore, Section 9.13 states that “the injection of chemical products must not be performed directly into the pools”. Section 9.14 allows the use of the following chemical disinfectants for pool water sanitation: • Chlorine-based disinfection systems (Type I treatment systems), including chlorine products and derivatives: sodium hypochlorite (NaOCl); calcium hypochlorite (Ca(ClO)2); liquid chlorine (Cl2, chlorine gas); products containing trichloroisocyanuric acid or sodium or potassium dichloroisocyanurate, or other isocyanuric acid derivatives, if their use is approved by health authorities. • Bromine-based disinfection systems (Type I treatment systems). • Ozone disinfection systems (Type II treatment systems). Additionally, Section 5.5 of the NP 4542:2017 [46] includes UV light as Type III treatment systems.
Finnish guidelines [32] stipulate that the microbiological quality of pool water must primarily be ensured through chlorination, avoid organic isocyanurate chlorides such as sodium chloroisocyanurate dihydrate, and favor disinfection with inorganic chlorine compounds. However, the use of alternative disinfection methods, such as ozonation or UV light, is also permitted to enhance the effectiveness of chlorination.
The Swedish HSLF-FS 2021:11 [50] mandates that pool water must be continuously purified and disinfected with an effective amount of disinfectant throughout the entire basin. Concurrently, the Guidance [49] outlines existing disinfection methods, emphasizing that chlorine currently best meets quality and safety criteria and remains the predominant disinfectant for swimming pools. However, the Guidance generally recommends that, when selecting a treatment and disinfection method, operators adhere to the principle of choosing the best Available technology, always considering the potential risks to human health.
The Danish Order BEK [54] stipulates that water in swimming pools not utilizing surface water must be recirculated, filtered, and disinfected. According to its § 9, the disinfection of pool water must be carried out using chlorine gas or a sodium hypochlorite solution. Conversely, water in swimming pools that uses surface water (including seawater) may not require disinfection.
As for the Norwegian regulation [55], which does not specify the use of seawater in swimming pools, it states that “each pool must always, and at every point within the circulation system, contain a sufficient amount of disinfectant to eliminate harmful microorganisms that pose a health risk, as well as to prevent the growth of organisms that, under particular circumstances, may cause diseases in humans”. Additionally, when disinfecting water with chlorine (or hypochlorite), specific quality requirements must be met.
The Dutch Environmental Decision (Bal) [56], while not addressing the use of seawater in swimming pools, specifies in Article 15.12 that it applies to pools where water is disinfected. It mandates that cyanuric acid must not be added to the water and that the use of ozone for water treatment must prevent ozone from entering the pool.
In Italy, the 2003 State-Regions Agreement [60] does not apply to pools supplied with seawater; however, it provides a comprehensive and detailed list of disinfectants, flocculants, and pH regulators approved for use in pools supplied with drinking water. Examples of such disinfectants include ozone, liquid chlorine, sodium hypochlorite, calcium hypochlorite, anhydrous sodium dichloroisocyanurate, hydrated sodium dichloroisocyanurate, and trichloroisocyanuric acid. The Agreement also stipulates that the use of substances not included in the lists must receive prior authorization from the Ministry of Health. Furthermore, the “Guidelines for the reopening of economic and productive activities 20/94/CR01/COV19” [66] whose current validity remains uncertain, state that “For seawater pools, where applicable, maintain disinfectant concentrations within the recommended limits and in compliance with international standards and regulations, preferably at maximum capacity limits. Alternatively, implement physical treatments at maximum capacity or ensure maximum water exchange within the limits of the maximum intake capacity”.
Analogous to Italy, the Albanian Regulation [67], which does not mention the possibility of using seawater for public pools, establishes a detailed list of substances that may be utilized as disinfectants, flocculants, and pH adjusters. The list of disinfectants is consistent with the Italian regulations and includes the following: ozone; liquid chlorine; sodium hypochlorite; calcium hypochlorite; anhydrous sodium dichloroisocyanurate; dihydrate sodium dichloroisocyanurate; and trichloroisocyanuric acid.
In Greece, disinfection requirements are stipulated both by the Health Ordinance Γ1/443/1973 [68] and by Circulars Δ1δ/ΓΠ.οικ. 57290/2019 [92] and ΔΥΓ2/99932/06/2007 [69]. When the text of [92] clarifies the permissible operating conditions for the recirculation, renewal, and disinfection systems of swimming pool water, the Circular [69] mandates that disinfection is obligatory in all cases of pool management, as explicitly specified in Article 18 of [68]. However, the operation of pools without disinfection is permitted only when there is a continuous influx of clean water from a safe natural source not subject to chlorination. Regarding disinfection methods, Article 18 states that the pool water must be continuously disinfected by the addition of chlorine using appropriate devices, in the form of an aqueous solution of gaseous chlorine, calcium hypochlorite, sodium hypochlorite, or chlorine produced by electrolysis, or any other approved chlorinated compound. Furthermore, the use of a disinfection method other than chlorine is permitted, subject to approval by the Health Authority, provided that it ensures complete disinfection. Regarding seawater, Law 5170/2025 [7], while allowing its use in pools within legally operating hotel facilities, does not provide specific details concerning its disinfection.
In Bulgaria, “Instruction No. 34” [70], despite not mentioning the possibility of using seawater in swimming pools, stipulates in Article 33 that pool water may be utilized for a maximum of 45 days, provided that it is recirculated through functioning purification systems and is regularly disinfected. In the absence of such systems, or if the existing systems are non-operational, the water must be completely replaced on a weekly basis and disinfected regularly.
Estonian Regulation No. 80 [71] stipulates that pool water must be treated through filtration and disinfection processes. It also allows for purification methods such as coagulation, activated carbon treatment, ultraviolet radiation, and ozonation. Furthermore, to disinfect pool water, it indicates that only disinfectants compliant with the Biocidal Regulation [95] may be used, ensuring that their application and quantity do not compromise the water’s properties or pose a risk to human health.
In Malta, where the legislation 545.07 [73] permits the use of seawater in swimming pools located within one hundred meters of the coastline, concurrently, “Swimming pool regulation, 2005” [72] delineates the disinfectants used in pools, categorizing them based on the frequency of application. The most used disinfectants in large swimming pools are chlorine-based compounds, which include gaseous chlorine, calcium and sodium hypochlorite, sodium dichloroisocyanurate, electrolytic generation, ozone–chlorine combination, and chlorine dioxide both as a standalone and in combination with chlorine. Bromine-based disinfectants are less frequently used, comprising liquid bromine, bromochlorodimethylhydantoin, and sodium bromide combined with hypochlorite. Rarely used disinfectants, typically employed for smaller pools, include bromide chloride, UV, UV–ozone combinations, iodine, hydrogen peroxide, silver/copper complexes, and biguanides. Furthermore, the notes in Annex I of [72] refer to non-disinfected pools; however, no guidance is given regarding the conditions under which pools may be undisinfected.
In Cyprus, the regulation KDP 368/96 [75], which does not reference the use of seawater in swimming pools, stipulates that pool water must be continuously disinfected through the addition of chlorine using an appropriate device in the form of an aqueous solution of chlorine gas or calcium hypochlorite or sodium hypochlorite, or chlorine produced by electrolysis or another approved chlorine compound. Furthermore, an alternative method for water disinfection may be employed, subject to the approval of the competent Health Service if it ensures complete disinfection.
More detailed information is provided in Table S1: An overview of the legislative framework in European coastal countries regarding the use of seawater in swimming pools and the disinfection methods required, as included in the Supplementary Material.
3.3. Peculiarities of Seawater Disinfection for Swimming Pool Use
Chlorinating seawater for use in swimming pools is a viable, albeit complex, prospect. Saltwater chlorination systems, which generate chlorine via the electrolysis of dissolved sodium chloride, may be adapted for seawater treatment. However, seawater’s high salinity and high ionic strength significantly increase the risk of material degradation. As a result, the implementation of such salt chlorination systems often requires the use of durable construction materials, such as stainless steels and titanium alloys [97], electrodes coated with ruthenium or iridium [98], along with corrosion-resistant polymers, e.g., polymer composites [99]. While these materials enhance durability and extend service life, they also raise initial investment costs, potentially limiting accessibility for smaller operators in the absence of public incentives. Despite increasing interest in seawater use, comprehensive cost–benefit analyses comparing conventional and salt-resistant disinfection systems under operational conditions are lacking. Further research is needed to support evidence-based decisions regarding their technical and economic viability.
Alternatively, conventional disinfection methods can be applied, and chlorinating agents can be directly added to seawater pools. However, the unique chemical profile, including the inherent mineral composition of seawater and equilibrium dynamics of seawater, may be altered, requiring adjusted dosing protocols. Moreover, the addition of traditional chlorine compounds may exacerbate pool infrastructure corrosion, adversely affecting its longevity, while maintaining a balance in water chemistry, e.g., pH, alkalinity, and calcium hardness, is more complex in saline matrices treated with direct chlorination.
In addition to disinfection, effective turbidity control and the removal of particulate and organic matter are critical in seawater pools. This requires robust filtration systems and durable materials throughout the infrastructure to ensure long-term operational integrity.
Regardless of the method employed, effective microbial control remains paramount for public health protection. Furthermore, compliance with local regulations governing seawater use and discharge, together with the environmental assessment of sourcing and disposal of seawater, is essential for sustainable implementation. While both approaches—the direct chlorination of seawater and the use of high-salinity-resistant saltwater chlorination systems—are technically viable, the latter appears more promising for long-term application. Compared to direct chlorine addition, these systems may offer improved chemical stability, reduced infrastructure degradation, and more consistent water quality control. However, their successful implementation depends on thorough cost–benefit planning, appropriate technology selection, and strict adherence to regulatory frameworks, which necessitates harmonization across Europe [7,11,27].
3.4. Overview of Microbiological and Physicochemical Quality Requirements for Pool Water
To assess the water quality of swimming pools and the effectiveness of its treatment, it is essential to analyze both physicochemical and microbiological indicators. European national regulations or guides governing pool safety have established a framework of quality indicators that must be verified on-site for certain physicochemical parameters, such as color, odor, pH, turbidity, temperature, and free chlorine. These parameters provide valuable real-time information on water quality and its capacity to support bacterial growth. Furthermore, chemical and biological parameters requiring laboratory analysis are specified, along with monitoring frequency, sampling methods, and analytical procedures.
Analogous to the authorization for using seawater to fill pools and approved disinfection methods, the European legislative framework exhibits significant variation in the list of quality indicators to be monitored and their corresponding quantitative limits. This variability ranges from the breadth of parameters recommended for control to the different terminologies used for equivalent parameters, and the conditions under which the same parameter must be measured.
For example, the microbiological parameter “Cultivable microorganisms” [49] is also referred to as “Heterotrophic colony count” [32], “Bacterial count” [60] or “Colony-forming units” [38], with differing specifications regarding the conditions of measurement—such as after 24 [68] or 48 h [59], at temperatures of 36 [34], 37 [58], or 36 ± 2 °C [40], or without specified conditions [70]. And, for instance, a chemical parameter like “Oxidizability” may be represented as “KMnO4 consumption in heated solution under acidic conditions” [31] “Oxidizability of MnVII → MnII above that of filling water” [36], or simply “Potassium permanganate” [32].
Regarding the spectrum of microbiological parameters to be monitored, the situation varies across countries. Finland [32], for instance, requires the control only of basic parameters such as heterotrophic colony counts and Pseudomonas aeruginosa, while Lithuania and Estonia add, for example, Helminth eggs [41] or Mycobacterium spp. [71] to the wide spectrum of indicators to be monitored, including pathogenic Escherichia coli, whose monitoring is required by most European countries. To control Legionella [100], some countries require specific testing for Legionella pneumophila [47], while others monitor Legionella spp. [45], referring to it in various ways such as Legionella spec. [38] or simply Legionella [91].
Due to the complexity of summarizing the microbiological monitoring framework across 23 European countries, Supplementary Table S2: Microbiological parameters of pool waters regulated in European countries with sea access, provides the full range of parameters, citing them exactly as reported in the respective regulations. In summary, nearly all countries mandate the monitoring of total bacterial count, although varying incubation temperatures hinder direct comparison. Most require the absence of E. coli in 100 mL, and limits of 0–1 CFU/100 mL for P. aeruginosa are common. Legionella monitoring in hot tubs is also widespread, with acceptable levels ranging from 0 to 100 CFU/L. Other parameters—such as enterococci, Staphylococcus spp., sulfite-reducing Clostridium spores, and Cryptosporidium—are included inconsistently.
Similarly, the monitoring of physicochemical parameters presents a complex landscape. While core physicochemical parameters—such as temperature, pH, and free and combined or total chlorine—are widely required, others, e.g., TOC, redox potential, nitrates, ammonia, are regulated inconsistently across countries. Some countries, beyond the primary indicators, require the monitoring of additional substances such as arsenic [38] or radiological indicators [70]. Certain regulations, like those in France, specify not only permissible quality limits (QLs) but also the desired quality reference values (RVs) [34]. Typically, regulations do not specify quality indicators for the water used to fill pools, instead requiring that it meet drinking water standards. However, some regulations, such as those in France [35], establish specific criteria for source water if it does not come from the public water supply. Additionally, countries including Poland [36], Italy [60], and Albania [67] specify certain indicators for inlet water delivered to the pool via the circulation system.
A more complete overview of the physicochemical parameters required for swimming pool water monitoring according to European regulations, along with annotations of some parameters reported by researchers, and including ozone concentrations in air, is provided in the Supplementary Material, Table S3: Physicochemical parameters of pool water and air regulated in European countries with sea access.
3.5. Risk Assessment
Effective risk assessment and management strategies in swimming pools are essential for safeguarding public health. In countries such as Greece, where tourism represents a major economic sector, ensuring pool safety is a critical priority. Mplougoura et al. [101] conducted a detailed evaluation of potential hazards, classifying risks based on their likelihood and impact, and proposing appropriate mitigation measures. The authors also emphasized the importance of maintaining the reputation of recreational water facilities.
Risk assessment in seawater-filled pools—compared to freshwater pools—requires the consideration of a broader range of potential hazards associated with the use of saltwater in recreational facilities. One of the primary concerns involves the corrosive effects of salt on construction materials and infrastructure. However, this risk can be effectively mitigated by employing salt-resistant pool equipment and furnishings, as discussed in Section 3.3. In cases where seawater and freshwater are mixed to fill the pool, as reported by Nitter et al. [26], additional operational risks may arise. This practice can lead to physicochemical imbalances due to the differences in ionic strength and composition, potentially resulting in the precipitation of calcium carbonate, magnesium hydroxide, or other mineral salts. These precipitates may cause scaling, sedimentation [102], and impair filtration systems, ultimately compromising disinfection efficiency, as turbidity-associated particles can shield microorganisms from disinfectants [27]. Preventive operational measures may include the use of buffer tanks for controlled blending, reverse osmosis desalination systems, or chelating agents, along with the strict monitoring of water chemistry and pH.
The next critical issue is the proliferation of microorganisms in water taken from surface sources, including both naturally occurring aquatic flora and pathogenic organisms introduced via wastewater discharge or fecal contamination from humans or animals. These microbial risks are exacerbated by elevated water temperatures and inadequate disinfection practices. Such risks can be reduced by effective disinfection strategies, such as saltwater chlorination via electrolysis. For example, Gregg et al. [25] demonstrated that even methicillin-resistant Staphylococcus aureus is rendered non-viable in seawater pools after chlorination.
Therefore, the disinfection of pool water is essential, but disinfectants react with organic and inorganic matter present in the water, forming DBPs that may pose health risks to users and staff [12,22]. The toxic action pathways of DBPs may vary depending on several factors, including the route of exposure, DBP chemical structure, dose and duration of exposure, metabolic activation, target cell/organ type, swimmer’s respiratory rate, and individual physiological factors [16,103]. DBPs can induce oxidative stress, generate reactive oxygen species, and form DNA adducts, leading to DNA damage, particularly in HepG2 cells, thus increasing their genotoxic potential [8]. Some DBPs are metabolically activated by enzymes such as glutathione S-transferase theta-1 (GSTT1-1), resulting in mutagenesis [13]. In vitro studies have shown that DBPs can induce chromosomal aberrations, sister chromatid exchanges, and micronuclei formation [9], all of which contribute to their carcinogenic potential. Additionally, several DBPs exhibit cytotoxic and teratogenic properties [8,9,10,11,12,13,14,15].
The concentration and nature of DBPs in pools depend on multiple factors, including the type and concentration of disinfectants, pool characteristics, users’ hygiene practices, the intended use of the pool (e.g., for sports, relaxation, or recreational activities), filling water source (freshwater, seawater or thermal water), and pool pH [8,9,16]. The most identified DBPs in pools include trihalomethanes (THMs), haloacetic acids (HAAs), haloamines (HAs), haloacetonitriles (HANs), haloaldehydes (HALs), haloketones (HKs), haloamides (HAMs), halophenols, haloquinones, and N-nitrosamines [16,20].
Seawater has a unique chemistry, characterized by its pH, which is generally higher than those of freshwater, and elevated bromide (Br−) concentration (approximately 67 mg/L on average, but ranging from 15 mg/L in the Baltic Sea to 85 mg/L in the Mediterranean Sea, and reaching exceptional levels of 5.2 g/L in the Dead Sea) [22]. These bromide levels can pose significant challenges, particularly when chlorination is employed for disinfecting seawater pools. Bromide ions react with chlorine to form bromine (HOBr/OBr−), a predominant disinfectant and oxidizing agent in seawater pools, as shown in Equations (8) and (9) [89]:
HOCl + Br− → HOBr + Cl−, k = 6.8 × 103 M−1s−1
OCl− + Br− → OBr− + Cl−, k = 9.0 × 10−4 M−1s−1
These reactions result in the enhanced formation of brominated DBPs, which can increase chemical health risks for swimmers and workers [19]. Brominated DBPs are known to be more cytotoxic, genotoxic, and mutagenic than their chlorinated counterparts [9,11,19]. For example, monobromoacetic acid is approximately 280 times more cytotoxic and 47 times more genotoxic than monochloroacetic acid, as demonstrated by Hsieh et al. [104]. Bromate, another common DBP of both swimming pool water and potable water disinfection, is classified as a Category 1B [15] “presumed to have carcinogenic potential for humans”, according to the Regulation (EU) No. 1272/2008 (CLP) [105]. Furthermore, the higher pH levels of seawater pools compared to freshwater pools may also influence the formation of DBPs.
Despite this, most of the studies on DBP presence in pools focus on freshwater pools treated with chlorine-based compounds. Very few have investigated DBP speciation and concentration in seawater-fed pools. However, existing studies of Rhys et al. [9], Manasfi et al. [6,11], and Parinet et al. [13] show that HAAs are the dominant chemical class in both pools types. Röhl et al. [15] reported the bromate concentration up to 34 mg/L in some German disinfected swimming pools sourced with seawater. This concerning level was approximately an order of magnitude higher than bromate concentrations typically found in freshwater pools, exceeding the national limit of 2 mg/L [38].
Total trihalomethanes (i.e., sum of four THMs: chloroform, bromodichloromethane, dibromochloromethane, and bromoform) concentrations in reported studies are generally lower in chlorinated pools that also use ozone disinfection, compared to those using chlorine alone. In contrast, according to Rhys et al. [9], saltwater-chlorinated pools exhibit higher TTHMs concentrations on average. Nitter et al. [26] reported a 282% increase in 4TTHMs concentrations in a facility using 33% seawater mixed with freshwater, compared to the one using freshwater, likely due to different disinfectants’ ventilation systems. Concurrently, brominated DBPs dominate in seawater pools, while chlorinated DBPs species are more present in freshwater pools [11].
Risk assessment conducted by the Swedish Institute of Environmental Medicine suggests that the cancer risks associated with regular exposure to high concentrations of chloroform among swimmers can be minimized by maintaining its concentration below 100 µg/L [49]. But in seawater pools, the predominant THM species is bromoform, which, unlike chloroform, has not yet been classified as a Group 2B (possibly carcinogenic to humans) by the International Agency for Research on Cancer (IARC) [106].
Furthermore, Manasfi et al. [6] found that, according to the Ames test, freshwater pools exhibit higher mutagenicity compared to seawater pools, attributable to the higher DBPs levels in the former. Additionally, Granger et al. [107] quantified 60 DBPs in a public indoor pool before and after switching from freshwater to electrolytically chlorinated saltwater. The results revealed a 15% increase in total DBPs and a 73% increase in brominated DBPs after the saltwater system implementation. Despite these increases, cytotoxicity and genotoxicity, assessed using the TIC-Tox metric, decreased by 45% and 15%, respectively, due to the overall lower toxicity of the newly formed DBPs.
Chau et al. [16] stressed that the health benefits of swimming outweigh the risks associated with exposure to disinfection by-products, including those found in seawater pools. Nonetheless, it is important to note that toxicological data on brominated trihalomethanes and brominated DBPs are limited, and studies of the chemistry of disinfected seawater pools remain limited and require further investigation.
Table 2 summarizes the literature data on regulated DBPs in swimming pools across examined countries, including regulatory limits and their measured concentrations in seawater pools compared to freshwater pools. Four THMs currently represent the only class of organic DBPs regulated in pool water, as some of them, i.e., chloroform and bromodichloromethane, are classified as “possible human carcinogens” in Group 2B by IARC. The table also includes inorganic DBPs such as bromate, a suspected carcinogen, chlorite, and chlorate, which remain poorly regulated in pool water, although restricted in drinking water due to their toxicity [8]. Additionally, a volatile trichloramine, associated with respiratory issues and regulated in swimming pool air in some countries, is included. Supplementary Table S4 provides a more complete picture, including the water and air concentrations and cytotoxicity of other unregulated DBPs detected in seawater-fed pools, compared with being supplied with freshwater.
Table 2.
Concentrations of THMs and inorganic DBPs in the water and trichloramine in the air of freshwater and seawater pools, and the corresponding regulatory quality limits.
Table 2.
Concentrations of THMs and inorganic DBPs in the water and trichloramine in the air of freshwater and seawater pools, and the corresponding regulatory quality limits.
| Disinfection by-Product | Freshwater Pools | Seawater Pools | Ref. | DBPs Quality Limits in Pool Water and Air Set by Regulations | ||||
|---|---|---|---|---|---|---|---|---|
| Recom-Mended Value | Quality Limit | Country | Note from Regulation | Ref. | ||||
| Swimming pool water | ||||||||
| Total THMs (4TTHM), μg/L | 80.2 7–577 16.8–29.4 122.4–435.5 777 | 50.4–91.8 51.8–105.8 77.7–995.6 307.6–327.8 260–322 | [6] [9] [11] [12] [13] [18] [26] [107] | 20 | 100 | France | Keep as low as possible without affecting disinfection | [34] |
| 100 | Portugal | [48] | ||||||
| 20 (a) | Germany | For indoor pools. In outdoor SPs higher QL is permitted. | [38] | |||||
| 50 | Slovenia | [39] | ||||||
| 100 | Poland | [36] | ||||||
| 100 | Sweden | [50] | ||||||
| 25 50 | Denmark | -For indoor SPs with T ≤ 34 °C, -For SPs with T > 34 °C, outdoor SPs, hot tubs | [54] | |||||
| 50 (a) | The Netherlands | [56] | ||||||
| 100 | Croatia | For conventional pools | [40] | |||||
| Chloroform, μg/L | 69.8 0.2–243 | N.D. 0.1–6 0.1 (mean)–0.9 (max) 0.01–0.29 | [6,11] [9] [10] [13] | 20 30 | Poland | -For children up aged ≤3, -For other swimming pools | [36] | |
| 50 | Finland | Not applicable to outdoor SPs | [32] | |||||
| 100 | Lithuania | If chlorine-based compounds are used for disinfection | [41] | |||||
| Bromodichloromethane, μg/L | 7.9 0.13–167 | N.D. 0.29–5 0.3 (mean)—2.2 (max) 0.05–1.10 | [6,11] [9] [10] [13] | |||||
| Dibromochloromethane, μg/L | 1.9 0.49–120 | 1.6–5.2 3.57–27 18.9 (mean)—81.0 (max) 2.1– 5.5 3.2–63.6 | [6] [9] [10] [11] [13] | |||||
| Bromoform, μg/L | 0.6 0.04–47 | 48.9–86.7 50–651 300 (mean)—1029 (max) 49.7–101.3 73.5–930.7 | [6] [9] [10] [11] [13] | |||||
| Bromate, mg/L | 3 <0.02–5.0 | <0.2–34 | [9] [15] | 2 | Germany | [38] | ||
| 0.1 | The Netherlands | [56] | ||||||
| Chlorite, mg/L | 0.02–0.022 | [11] | 0.1 | Slovenia | In conventional pools, if ClO2 is used for water treatment | [39] | ||
| 0.4 | Croatia | [40] | ||||||
| Chlorate, mg/L | 0.04–37 | [11] | 30 | The Netherlands | [56] | |||
| Chlorite + chlorate, mg/L | 30 | Germany | [39] | |||||
| Swimming pool air | ||||||||
| Trichloramine, μg/m3 | 20–1340 <LOD–1700 | [11] [14] | 200 | Sweden | [50] | |||
| 500 | The Netherlands | [56] | ||||||
| 300 | 500 | Belgium, Flanders | Only for indoor SPs, except for indoor natural swimming pools | [31] | ||||
| 500 | 1000 | Belgium, Walloon | 500 is intervention value | [58] | ||||
| 300 | 500 | Belgium, Brussels | [59] | |||||
Notes: 4TTHM—sum of 4 trihalomethanes (chloroform, bromodichloromethane, dibromochloromethane, and bromoform); SPs—swimming pools; QL—quality limit; (a) calculated as chloroform; N.D.—not determined, T—water temperature; LOD—limit of detection.
Figure 2 illustrates the distribution of different classes of DBPs, identified in fresh- and seawater swimming pools. The percentages shown in the pie charts represent the relative abundance of each DBP class, calculated based on their average concentrations reported in Supplementary Table S4.
Figure 3 illustrates the concentrations of different classes of DBPs, identified in fresh and seawater swimming pools and their cytotoxicity (expressed as 1/LC50), based on values extracted from by Wagner et al. [108] and Qiu et al. [109]. Higher values along the trend line correspond to the greater cytotoxic potential of the respective DBP class. While it is recognized that the cytotoxicity of DBPs can be influenced by pH, affecting both chemical speciation and bioavailability [REF], the current analysis does not incorporate this dynamic factor, due to the lack of comprehensive LC50 data across varying pH conditions for all identified compounds. Future studies should aim to integrate pH-dependent cytotoxicity data to better reflect real-world exposure scenarios and improve the accuracy of risk assessments.
Table 2 highlights several critical issues. Firstly, approximately half of 23 European countries surveyed do not set regulatory limits for THMs, while the others set thresholds ranging from 20 to 100 μg/L. This is despite decades of scientific evidence on the health risks associated with THMs and the measured concentrations in both seawater and freshwater pools, which frequently exceed these limits, with brominated species being more prevalent in the former. Other classes of DBPs, i.e., HAAs, HALs, and HANs, known for their greater cytotoxicity compared to THMs, as confirmed by Figure 3, and detected at higher concentrations in freshwater pools than in seawater pools (Figure 2 and Supplementary Table S4), are not currently regulated. Concurrently, exposure to airborne trichloramine, while data are lacking for seawater pools, often exceeds the recommended average limit of 500 mg/m3 in freshwater facilities. Of particular concern is the frequent exceedance of bromate limits, especially in seawater pools. Although the systemic relevance of some exceedances remains uncertain due to limited data, this highlights the urgent need for regulatory attention.
Regulatory gaps regarding the chemical safety of pool water may reflect an overemphasis on microbiological standards, pushing operators to prioritize disinfection efficiency. This can inadvertently result in elevated DBP levels, particularly in seawater pools, where organic and bromide loads are higher. In addition to the implications of fragmented and inconsistent regulations regarding sources for pool supply and disinfection methods, (see Section 3.1), the institutional underestimation of DBP-related risks may limit investments in scientific research and innovation, limiting progress in sustainable water treatment technologies, essential to public and environmental health.
Environmental risks associated with the discharge of saline and disinfected water containing residual disinfectants, free chlorine, or DBPs into municipal wastewater systems or directly into marine environments must also be considered. Due to concerns about the ecological impact of cruise ship wastewater [27] and ballast water from cargo vessels, recent studies have explored the release of DBPs into the aquatic environment. Certain DBPs have been shown to inhibit algal photosynthesis, while others promote cyanobacterial proliferation, both with potentially harmful ecological consequences [110]. However, studies on DBP accumulation in marine sediments remain limited. Despite growing awareness, environmental regulations rarely address DBP discharges, underscoring the need for targeted monitoring and ecotoxicological assessment in coastal areas, and the adoption of effective treatment technologies to mitigate the environmental impacts of DBPs.
4. Conclusions
In the context of the growing attention paid to water resilience strategies, enhancing the efficiency and sustainability of water use in swimming pools through alternative sources such as seawater requires the careful evaluation of both public health and environmental implications. However, as highlighted in this review, the regulatory landscape governing swimming pools across 23 European coastal countries remains fragmented. Only a few countries explicitly permit the use of seawater, and regulatory inconsistencies persist in the disinfection practices of recreational water facilities, with limited consideration given to the specific challenges posed by seawater treatment.
Likewise, microbiological and physicochemical parameters are inconsistently regulated, and significant gaps remain in the regulation of DBPs, despite their known potential human risks. This lack of regulatory harmonization not only affects public health protection but also hinders innovation towards more sustainable water use and treatment, aligned with human health protection and environmental safety.
The findings suggest that the use of seawater in swimming pools is technically feasible, and high-salinity-resistant saltwater chlorination systems appear to be a more pragmatic disinfection approach. Nevertheless, effective implementation requires long-term cost–benefit assessment (not addressed in this work) and rigorous regulatory compliance to ensure both safety and operational reliability, which in turn demands harmonization.
This study is limited to public swimming pools within the European coastal region and does not include private facilities or non-European regulations, which may be explored in future research. Furthermore, due to language barriers, some recent national regulation updates may have been unintentionally overlooked. Another limitation concerns the DBP risk assessment, which solely focused on literature-based cytotoxicity data, without addressing mutagenicity or pH-related speciation dynamics in seawater.
Further research is essential to fully understand the chemical and environmental implications of seawater pool operations and could focus on the following aspects:
- Development and optimization of seawater disinfection methods: Comparative experimental studies using pilot-scale pools filled with real seawater matrices should assess the effectiveness of hybrid disinfection approaches in minimizing DBP formation under high and varying salinity and organic load conditions;
- Quantitative risk assessment models for DBP exposure in marine environments: Environmental impact assessments should be supported by the field sampling of water and sediments near pool discharge sites, coupled with targeted chemical analyses using both conventional techniques (e.g., chromatography coupled with mass spectrometry) and innovative, rapid methods (e.g., near-infrared spectroscopy), and covering both regulated and emerging DBPs;
- The longitudinal monitoring of swimmer health outcomes, especially concerning brominated, iodinated, and emerging DBPs, to better characterize the health risk profiles of seawater-specific DBPs;
- Life cycle assessment (LCA) and cost–benefit analyses: Quantitative evaluations of the sustainability of the corrosion-resistant materials for seawater pool systems should be carried out using standardized LCA frameworks and techno-economic models to assess resource use, operational costs, and environmental impacts.
Finally, the COVID-19 pandemic, when each country has implemented different public health protocols to address emerging threats such as SARS-CoV-2, has underscored the need for a unified legislative framework to ensure swimming pools’ safety in response to emerging threats. The development of harmonized European regulations for swimming pools’ water quality, analogous to those for drinking water, is essential to ensure consistent safety standards across Member States. A common legal basis for risk assessment would strengthen public health and environment protection and support the safe adoption of innovative technologies in pools, including those using seawater.
Supplementary Materials
The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/w17172544/s1, Table S1: An overview of the legislative framework in European coastal countries regarding the use of seawater in swimming pools and the disinfection methods required; Table S2: Microbiological parameters of pool waters regulated in European countries with sea access; Table S3: Physicochemical parameters of pool water and air regulated in European countries with sea access; Table S4: Concentrations of DBPs in the water and air of freshwater and seawater pools and quality limits by the regulations in European countries with sea access; Table S5: Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist.
Author Contributions
Conceptualization, T.P., A.M. and V.R.S.; methodology, T.P. and F.V.; software, F.V.; validation, G.D.M., F.N.D.G., E.V., E.F. and A.M.; formal analysis, T.P. and G.D.M.; investigation, T.P., G.D.M., F.N.D.G. and F.V.; data curation, T.P. and E.F.; writing—original draft preparation, T.P., A.M. and V.R.S.; writing—review and editing, T.P., G.D.M., F.N.D.G., F.V., E.V., E.F., A.M. and V.R.S.; visualization, T.P., G.D.M., F.N.D.G., F.V., E.V., E.F., A.M. and V.R.S.; supervision, V.R.S. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Data Availability Statement
Data supporting the findings of this study are Available in the Supplementary Materials. Additional data that are not publicly Available due to restrictions (e.g., institutional policy or ongoing analyses) can be obtained from the corresponding author upon request.
Acknowledgments
ICSPS “International Conference on Swimming Pools and Spas” network and “AQUAE!” Public Engagement Initiative of the University of Rome “Foro Italico”, for discussion and feedbacks.
Conflicts of Interest
The authors declare no conflicts of interest.
Abbreviations
The following abbreviations are used in this manuscript:
| DBPs | Disinfection by-products |
| THM | Trihalomethane |
| TTHMs | Total trihalomethanes |
| SP | Swimming pool |
| SPs | Swimming pools |
| QL | Quality limit |
| RV | Reference value |
| Ref. | References |
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Figure 1.
Graphical summary of the legislative framework in Europe regarding seawater use in SPs. ![Water 17 02544 i001]( "Water 17 02544 i001")
—countries where regulations explicitly permit and regulate seawater use; ![Water 17 02544 i002]( "Water 17 02544 i002")
—countries where regulations indirectly mention seawater use; ![Water 17 02544 i003]( "Water 17 02544 i003")
—countries where seawater use is neither expressly regulated nor forbidden; ![Water 17 02544 i004]( "Water 17 02544 i004")
—countries where regulations allow seawater use but explicitly delegate governance to regional legislation; ![Water 17 02544 i005]( "Water 17 02544 i005")
—countries whose legislation allows the use of seawater in some facilities, without specifying its quality criteria; ![Water 17 02544 i006]( "Water 17 02544 i006")
—countries whose regulations have not been examined.
—countries where regulations explicitly permit and regulate seawater use; 
—countries where regulations indirectly mention seawater use; 
—countries where seawater use is neither expressly regulated nor forbidden; 
—countries where regulations allow seawater use but explicitly delegate governance to regional legislation; 
—countries whose legislation allows the use of seawater in some facilities, without specifying its quality criteria; 
—countries whose regulations have not been examined.
Figure 1.
Graphical summary of the legislative framework in Europe regarding seawater use in SPs. ![Water 17 02544 i001]( "Water 17 02544 i001")
—countries where regulations explicitly permit and regulate seawater use; ![Water 17 02544 i002]( "Water 17 02544 i002")
—countries where regulations indirectly mention seawater use; ![Water 17 02544 i003]( "Water 17 02544 i003")
—countries where seawater use is neither expressly regulated nor forbidden; ![Water 17 02544 i004]( "Water 17 02544 i004")
—countries where regulations allow seawater use but explicitly delegate governance to regional legislation; ![Water 17 02544 i005]( "Water 17 02544 i005")
—countries whose legislation allows the use of seawater in some facilities, without specifying its quality criteria; ![Water 17 02544 i006]( "Water 17 02544 i006")
—countries whose regulations have not been examined.
—countries where regulations explicitly permit and regulate seawater use; —countries where regulations indirectly mention seawater use; —countries where seawater use is neither expressly regulated nor forbidden; —countries where regulations allow seawater use but explicitly delegate governance to regional legislation; —countries whose legislation allows the use of seawater in some facilities, without specifying its quality criteria; —countries whose regulations have not been examined.
Figure 2.
Distribution of DBP classes identified in freshwater pools (a) and seawater pools (b).
Figure 3.
Cytotoxicity of DBP classes and their concentrations in freshwater pools (a) and seawater pools (b).
Figure 3.
Cytotoxicity of DBP classes and their concentrations in freshwater pools (a) and seawater pools (b).
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MDPI and ACS Style
Pobat, T.; Mandilara, G.D.; Nigro Di Gregorio, F.; Valeriani, F.; Veschetti, E.; Ferretti, E.; Mavridou, A.; Romano Spica, V. Pool Safety Regulations in Europe: Challenges Towards a Framework for Sustainable Seawater Utilization in Public Swimming Pools. Water 2025, 17, 2544. https://doi.org/10.3390/w17172544
AMA Style
Pobat T, Mandilara GD, Nigro Di Gregorio F, Valeriani F, Veschetti E, Ferretti E, Mavridou A, Romano Spica V. Pool Safety Regulations in Europe: Challenges Towards a Framework for Sustainable Seawater Utilization in Public Swimming Pools. Water. 2025; 17(17):2544. https://doi.org/10.3390/w17172544
Chicago/Turabian StylePobat, Tatsiana, Georgia D. Mandilara, Federica Nigro Di Gregorio, Federica Valeriani, Enrico Veschetti, Emanuele Ferretti, Athena Mavridou, and Vincenzo Romano Spica. 2025. "Pool Safety Regulations in Europe: Challenges Towards a Framework for Sustainable Seawater Utilization in Public Swimming Pools" Water 17, no. 17: 2544. https://doi.org/10.3390/w17172544
APA StylePobat, T., Mandilara, G. D., Nigro Di Gregorio, F., Valeriani, F., Veschetti, E., Ferretti, E., Mavridou, A., & Romano Spica, V. (2025). Pool Safety Regulations in Europe: Challenges Towards a Framework for Sustainable Seawater Utilization in Public Swimming Pools. Water, 17(17), 2544. https://doi.org/10.3390/w17172544
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