Unlocking the Potential of Reclaimed Water: Analysis of the Challenges and Market Size as a Strategic Solution for Water Scarcity in Europe

Abstract

The reclaimed water sector is poised for significant growth driven by urbanization, technological advancements, and increasing demand for alternative water sources, with an emphasis on improving treatment capacities and promoting water reuse for various applications. This study examines the challenges and market potential of reclaimed water as a strategic solution to address water scarcity in Europe, assessing the regulatory framework, associated risks, and reuse potential. A multi-phase analysis was conducted, including a review of the European directives, an analysis of water scarcity, an evaluation of wastewater reuse potential, identification of risks and technological challenges, and segmentation of the reclaimed water market across various European regions. Results highlight the significant underutilization of treated wastewater in Europe; only about 3% of urban wastewater is reused, equal to 1 billion m³/year (2.4% of effluent, <0.5% of freshwater withdrawals). Wastewater is often regarded as a pollutant rather than a resource; yet, advances in recycling and treatment technologies have increased safety and efficiency, making it a practical solution to water scarcity while strengthening climate resilience. At the strategic level, the study concludes that Europe holds strong potential for water recovery and a substantial opportunity to tackle water scarcity through innovative recovery solutions, thereby contributing to sustainability, fostering a circular economy, and promoting planetary health.

1. Introduction

The market size in the reclaimed water sector has become increasingly significant due to growing water scarcity worldwide, innovations in water purification technologies, and evolving regulatory frameworks. Currently, significant portions of reclaimed water are utilized for non-potable purposes, which include various applications such as agricultural irrigation and landscape management. Specifically, non-potable reuse strategies account for a substantial part of the water reuse landscape, with approximately 97.7% of total water reuse allocated to these applications, primarily for irrigation, which comprises around 52% of this total [1,2]. The upward trend in reclaimed water use is accelerating, with various nations adopting innovative technologies for water purification and reclamation. Countries such as the United States and Saudi Arabia are leaders in total wastewater reuse, while nations like Israel and Qatar are notable for their per capita usage of reclaimed water. This adoption aligns with increasing urban water demand and the necessity for efficient water management solutions in arid climates [2,3]. Membrane-based processes have been employed to enhance water reclamation, ensuring that the resulting water meets safety standards for irrigation and industrial applications [1,4].

Financially, the reclaimed water sector showcases distinct economic dynamics. Studies indicate that reclaimed water pricing models can sometimes align closely with potable water costs, often around 75% of potable water prices for reclaimed supplies [3]. Such pricing structures can influence utility adoption rates and market penetration, as municipalities and industries assess the cost–benefit ratio of investing in reclaimed water systems versus traditional water supplies. The sector’s financial viability is driven by the growing recognition of the socio-economic benefits of water reuse, especially in agricultural contexts where reclaimed water serves as a vital resource amidst increasing food production pressures [5,6].

Challenges within the reclaimed water market persist, driven by both technological and environmental considerations. The effectiveness of treatment technologies affects the safety and public perception of reclaimed water. Contaminants of emerging concern, including pharmaceuticals and pathogens present within reclaimed water, have prompted significant research into treatment innovations and best practices [7,8]. Furthermore, climate change implications on water reclamation practices introduce both challenges and opportunities, as it heightens awareness of water scarcity but complicates existing management systems through potential alterations in water quality and availability [5,9]. Regarding irrigation specifically, reclaimed water usage offers a solution to the vast freshwater allocation required for agricultural activities, accounting for nearly 70% of global freshwater use [10]. Implementing reclaimed water can significantly relieve stress on freshwater resources, promoting a shift towards more sustainable agricultural practices. Countries facing acute water scarcity are increasingly adopting reclaimed water as a critical alternative, thereby enhancing their resilience against climate variability [11,12]. Viewed through a planetary health lens, reclaimed water couples human water security with ecosystem integrity by lowering freshwater abstraction, pollutant loads, and climate-sensitive supply risks.

Market estimates indicate that the reclaimed water sector is poised for substantial growth as urbanization and demographic pressures escalate the need for alternative water sources. Innovations in membrane technology and biological treatment processes improve wastewater treatment facilities’ capacities, enhancing water quality outputs and fostering broader societal acceptance of reclaimed water for various uses, including potential direct potable applications [10,13]. Decentralized and nature-based solutions (NbS), such as constructed wetlands, subsurface wastewater infiltration systems, and vegetated drainage ditches that harness natural processes, are recognized for their sustainability and efficiency in wastewater treatment, as well as their potential for nutrient recovery [14,15]. The evolving landscape of regulations and technological advancements is likely to further shape the growth trajectory of the reclaimed water market, presenting numerous opportunities for investment and infrastructure development [16,17]. Infrastructure investments and public health measures are essential components of this market’s growth. Urban water management strategies increasingly emphasize integrating reclaimed water systems within broader hydrological cycles, promoting efficient use while addressing public health concerns regarding contaminants [16]. Effective management and mitigation strategies are crucial for maximizing the potential of reclaimed water while safeguarding public health, supported by rigorous monitoring of water quality [7,8].

In this context, global water demand is anticipated to grow by approximately 1% per year until 2050, leading to an increase of 20–30% over current usage levels. This growing demand, combined with environmental limitations and prolonged droughts due to climate change, has compelled many regions to explore alternative water sources, such as treated wastewater for non-potable applications. Despite these efforts, more than 2 billion people currently live in areas experiencing high water stress, and nearly 4 billion experience severe water scarcity for at least one month each year [18]. From 2000 and 2021, droughts impacted more than 1.4 billion people, causing the death of nearly 21,000 individuals [19].

Specifically in Europe, among available alternatives, reclaimed water stands out for its lower energy demands and greater cost-efficiency when compared to desalination or long-distance water transfers. According to the European Environment Agency (EEA), treated wastewater represents a more affordable option for increasing water supply capacity. Despite having a robust wastewater treatment infrastructure, the European Union (EU) continues to underutilize its potential for water reuse. Current estimates indicate that only about 2.4% of treated wastewater is reused across the EU [20], revealing a considerable opportunity to reposition treated effluents as a vital asset for enhancing climate resilience and water availability.

A critical dimension for the large-scale implementation of reclaimed water solutions lies beyond technology and regulation, encompassing public acceptance, economic feasibility, and governance frameworks. Public perception is often influenced by concerns over health risks and water quality, making transparent risk communication, awareness campaigns, and stakeholder engagement strategies essential to build trust and normalize reclaimed water use. From an economic perspective, high upfront investment costs, pricing models that may compete with conventional water supplies, and uncertainties in long-term returns represent persistent barriers, particularly for municipalities and agricultural users. Governance frameworks play a decisive role in overcoming these challenges by establishing clear regulatory pathways, harmonizing standards, and incentivizing adoption through financial instruments and policy support. Effective communication strategies that highlight safety assurances, economic benefits, and environmental gains are therefore indispensable to foster user confidence, reduce resistance, and accelerate the integration of reclaimed water into mainstream water management practices.

In alignment with these challenges, the EU has undertaken a comprehensive revision of its environmental and water legislation, with the objective of harmonizing existing directives with the escalating pressures of climate change, water scarcity, and environmental degradation. This regulatory reassessment includes the revision of the Urban Waste Water Treatment Directive (UWWTD) [21] and the Water Framework Directive (WFD) [22], as well as the development of new regulations specifically targeting water reuse and contaminant control. These efforts reflect the EU’s ambition to establish more stringent quality standards and risk-based approaches, ensuring not only environmental protection but also public health and resource sustainability. Within this context, the promotion of treated wastewater reuse has gained increasing attention, both as a mitigation measure and as a strategic component of circular water management.

This study aims to quantify the underexploited market potential for reclaimed water in the EU and identify regulatory and technological pathways to accelerate its adoption. The main objective is to analyze the challenges and market potential of reclaimed water as a strategic solution to tackle water scarcity in Europe. Unlike prior works focused solely on water reuse technologies or policy reviews, this study integrates geospatial treatment data, legislative analysis, and economic estimations to define regional market potential in reclaimed water.

European Regulatory Framework

In response to the increasing pressures caused by water scarcity and to ensure more sustainable water management, the European Union has progressively adapted its environmental legislation and introduced new legal frameworks. A key development in this regard is the adoption of Regulation (EU) 2020/741 [23], which sets the minimum requirements for safe water reuse in agricultural irrigation across Member States. This regulation, effective since June 2023, not only supports the EU Green Deal and Sustainable Development Goal 6 (SDG6 “Clean Water and Sanitation”), but also fosters a circular water economy. It aims to mitigate the impacts of water scarcity and reduce dependence on freshwater resources [24].

Regulation (EU) 2020/741 [23] defines reclaimed water as treated wastewater that has been collected through sewerage systems and processed in urban wastewater treatment plants (UWWTPs), followed by harmonized microbiological and chemical standards, specified in Annex I of the Regulation. Although its primary objective is to regulate agricultural irrigation, Article 2 allows Member States to authorize reclaimed water for other purposes, such as industrial reuse, as long as a high level of protection of both human and animal health, as well as the environment, is guaranteed [20]. Although the Regulation currently does not set threshold values for emerging pollutants (EPs), Articles 10 and 25 encourage their monitoring, anticipating future updates that may include limit values for pharmaceuticals and personal care products. Spain has taken a leading role with the enactment of Royal Decree (RD) 1085/2024 [25], which further tightens quality parameters for reclaimed water. It establishes more stringent thresholds for reclaimed water, particularly for microbiological indicators such as Escherichia coli (E. coli) (Annex I), as well as turbidity, total suspended solids, and biochemical oxygen demand (BOD5), exceeding even the minimum EU requirements defined in Annex I of Regulation (EU) 2020/741 [23]. These enhanced criteria compel Spanish wastewater treatment plants (WWTPs) to modernize and reinforce their tertiary treatment systems to ensure compliance and enable safe reuse, especially in agricultural applications.

Another major legislative update is the Directive (EU) 2024/3019 [26], which revises the Urban Wastewater Treatment Directive 91/271/EEC. This new Directive enhances the monitoring and treatment obligations of WWTPs across the EU. Article 21 introduces requirements for monitoring EPs, microplastics, resistant pathogens, viruses, and antibiotic-resistant bacteria, while Annex I details minimum monitoring frequencies and detection limits. This Directive also prioritizes the energy neutrality of WWTPs and integration with the polluter-pays principle for industrial discharges.

This evolving regulatory framework provides a strategic solution for WWTPs aiming to meet stricter treatment and reuse requirements. The deployment strategy prioritizes WWTPs that currently employ tertiary treatment for nutrient removal as the primary targets for integrating new quaternary or advanced tertiary treatment technologies. These advanced technologies can improve the microbial quality of treated effluents, ensuring compliance with stringent discharge standards for water bodies and agricultural reuse, as specified in Regulation (EU) 2020/741 [23]. This approach is particularly relevant in countries like Spain, where substantial investments have been made in water reclamation infrastructure. Existing or new facilities that lack tertiary treatment or are not expected to implement it will need to modernize their infrastructure to comply with both Directive (EU) 2024/3019 [26] and the quality standards set in RD 1085/2024 [25].

The potential market associated with these scenarios is influenced by several factors. One key aspect is the current proportion of the population served by sewerage and wastewater treatment systems across Europe. This includes both existing treatment plants and those that need to be constructed or upgraded to meet the requirements of Directive (EU) 2024/3019 [26] and Directive (EU) 2020/741 [23], as well as the treatment capacity and levels of treatment achieved (secondary, tertiary, etc.). Additionally, the potential market will be affected by the availability of freshwater in various geographical regions, as well as the availability of treated wastewater, which can be reclaimed and reused.

2. Methodology

The present study aims to investigate the European Union’s capacity to address the challenge of reclaimed water reuse. To achieve this, the study was conducted in several phases. First, as presented in Section European Regulatory Framework above, the European regulatory framework was examined to understand the existing guidelines and regulations governing water reuse in Europe. Next, in Section 3.1, the current state of water scarcity in Europe was analyzed, studying the Water Exploitation Index Plus of various European countries, identifying the main affected areas and factors contributing to this issue, and emphasizing the need to open the market to reused water.

The methodology applied in Section 3.2 consisted of a quantitative analysis of freshwater availability and use across Europe, combining sectoral demand data with national resource statistics. First, global and European sectoral water withdrawal patterns were reviewed, using figures from the literature and the EEA to characterize demand in agriculture, industry, domestic supply, and energy production. Next, long-term average freshwater resources by country were compiled from Eurostat and related databases, distinguishing between internal and external flows, and calculating per capita freshwater availability. Trends in total freshwater abstraction between 2000 and 2022 were examined, with particular attention to shifts between surface and groundwater sources and the sectoral redistribution of demand. Additional data on groundwater contributions to public and agricultural supply, as well as sectoral water use profiles, were incorporated to highlight the dependence of economic activities on water resources. Finally, these results were contextualized by linking observed pressures on freshwater systems with the potential role of wastewater reuse as a sustainable alternative to reduce abstraction and meet rising water demand.

In Section 3.3, the main risks associated with reclaimed water were examined in detail, with particular emphasis on the presence of emerging contaminants, as well as microbial risks linked to pathogens and antimicrobial resistance. Subsequently, in Section 3.4, the challenges in current wastewater treatment processes were analyzed, focusing on the technological limitations of conventional treatment methods in removing complex pollutants, and the operational constraints that hinder the large-scale adoption of advanced treatment solutions.

The methodology applied in Section 3.5 involved a comprehensive review and integration of European and national datasets, legislative frameworks, and case studies to assess the current capacity and potential of wastewater treatment and reuse. Data from Eurostat, the European Environment Agency, and national reports were used to quantify wastewater generation, treatment levels (primary, secondary, and tertiary), and reuse volumes across Member States. Regulatory analysis focused on the Urban Wastewater Treatment Directive (UWWTD) and its recent revision (Directive (EU) 2024/3019) [26], highlighting compliance obligations and future targets for micropollutant removal and energy neutrality. This approach identified gaps, challenges, and opportunities to expand wastewater reuse for water security, environmental protection, and EU Green Deal goals.

In Section 3.6, the results of the study on treated and reclaimed wastewater in Europe were presented, analyzing official data from Eurostat and segmenting the market across different regions within Europe. To facilitate the analysis, the results were grouped by European regions (Northern, Central, Southern, Eastern, and South-Eastern), providing a detailed and specific view of the situation in each region.

Finally, in Section 3.7, the potential market for reclaimed water in Europe was defined, analyzing the challenges, opportunities, and underutilization of treated effluents as a strategic resource to address water scarcity and enhance climate resilience, within the context of water as a resource. The methodology applied focused on estimating this potential market by integrating quantitative data and comparative analysis. Wastewater generation volumes were obtained from the WISE Freshwater Platform and expressed in million cubic meters per day, covering both domestic and selected industrial sources across urban agglomerations. These daily figures were extrapolated to annual values by multiplying by 365, yielding country-specific wastewater generation profiles. This dataset was then compared with official statistics on treatment and reuse levels reported by Eurostat and the European Environment Agency to identify current reuse rates and regional disparities.

3. Results and Discussion

3.1. Water Scarcity in Europe

Freshwater availability across Europe is highly variable and strongly influenced by climatic conditions, population density, and transboundary water flows. To assess the sustainability of freshwater use, the Water Exploitation Index Plus (WEI+) is commonly used. It measures the proportion of renewable freshwater resources used within a given area and time period. WEI+ above 20% signals water stress, and values above 40% indicate severe water stress and potentially unsustainable use [27].

According to the EEA, in 2022, approximately 34% of the EU population and 40% of its land were affected by seasonal water stress. Countries with the highest WEI+ values included Cyprus (91.8%), Malta (60.8%), Portugal (38.6%), Greece (33.6%), Spain (33.3%), Romania (32.5%), and Italy (30.9%) (Figure 1). These countries, primarily in Southern Europe, are among the most vulnerable to prolonged droughts and climate-related water stress [27].

Between 2000 and 2022, droughts impacted on average 167,000 km² annually (equivalent to 4.2% of EU land), due to low precipitation, high evapotranspiration and rising temperatures [28]. Despite a 19% reduction in total water abstraction across the EU between 2000 and 2022, the extent of areas affected by water scarcity has not declined, and the situation has deteriorated since 2010. This is particularly evident in Southern Europe, where around 30% of the population lives in regions experiencing permanent water stress and up to 70% face seasonal water shortages, especially during the summer months. This trend is expected to intensify due to climate change, which will likely increase the frequency, duration and severity of droughts. Without additional interventions, water scarcity will continue to worsen by 2030, compromising water availability for agriculture, industry and human consumption [27].

In Southern and Eastern Europe, where water demand for agriculture, tourism and energy continues to rise (Figure 2), approximately 52 million EU citizens already reside in water-scarce regions, according to the European Commission Joint Research Center [29]. Among them, Spain is particularly affected, with over 24 million people (50% of its population) exposed to permanent or seasonal shortages, followed by Italy (26%), Greece (49%) and Portugal (41%). Notably, Cyprus and Malta face national-level water scarcity year-round with WEI+ values well above 40% [27].

3.2. Freshwater Resource Availability and Use

Water demand differs globally and within Europe, with agriculture accounting for about 70% of freshwater withdrawals, industry less than 20%, and domestic use around 12%. Domestic demand, however, has grown most rapidly due to population growth, urbanization, and expanded sanitation, a trend expected to continue. Figure 3 shows global withdrawals from 1960 to 2020: domestic use rose by over 600%, compared to 250% in industry, 200% in irrigation (stabilizing after 2000), and 50% in livestock. Overall withdrawals more than doubled, underscoring the disproportionate rise in domestic demand and the strategic role of reclaimed water in alleviating urban pressures [19].

Approximately 80% of freshwater consumption in Europe comes from rivers and groundwater, both of which are highly vulnerable to overexploitation and pollution. According to data from the EEA, economic activities consume an average of 243,000 hm³ of water annually, with over 140,000 hm³ returned to the environment, although often it contains hazardous substances or pollutants, reducing the quality and usability of the resource [31]. As shown in

Table 1. Freshwater resources (million m³) across the EU—long-term annual average [33].

Country	Internal Flow 1	External Flow	Total Freshwater Resource	Freshwater Resources (m3/Inhabitants)
Austria	56,700	29,300	:	:
Belgium	11,288	10,563	25,011	2141
Bulgaria	15,884	83,957	99,841	15,029
Croatia	24,530	93,783	118,313	30,678
Cyprus	374	0	374	409
Czech rep	14,372	829	15,201	1424
Denmark	16,340	0	16,340	2768
Estonia	12,347	:	12,374	9153
Finland	107,000	3200	110,000	19,798
France	200,860	11,000	206,236	3030
Germany	104,000	69,000	173,000	2064
Greece	60,000	12,000	72,000	6898
Hungary	5580	91,500	97,080	:
Ireland	51,308	3526	54,834	10,615
Italy	133,455	:	133,455	:
Latvia	19,647	16,992	36,639	19,495
Lithuania	14,018	8552	22,539	7960
Luxembourg	905	739	1644	2517
Malta	83	0	83	156
Netherlands	9706	78,355	88,061	4975
Poland	50,319	7504	57,823	1570
Portugal	38,593	35,000	73,593	7154
Romania	39,285	284	39,569	2077
Slovakia	14,081	66,086	80,192	14,763
Slovenia	16,422	15,074	31,496	14,912
Spain	100,396	0	100,396	2102
Sweden	170,330	14,678	194,750	18,570
UK	161,369	6454	172,861	2935

¹ The Internal Flow is obtained by the difference between precipitation and evapotranspiration.

, the highest amounts of freshwater resources in Europe are found in Croatia (30,700 m³ per capita), followed by Finland (19,800 m³), Latvia (19,500 m³), and Sweden (18,600 m³) [32].

In the 27 EU Member States, total freshwater abstraction declined by 19% between 2000 and 2022, decreasing from 242,000 million m³ to 197,000 million m³ per year. Despite this overall reduction, there are marked sectoral differences and a shift in reliance on distinct water sources. Whereas surface water represented 80% of abstraction in 2000, it accounted for 74% in 2022, while groundwater increased from 20% to 26%. This shift is primarily attributed to the rising demand in the public water supply sector (+18%) and in agriculture (+17%), particularly in Southern Europe [19].

Currently, groundwater supplies 62% of public water demand and 33% of agricultural water demand in the EU [34]. Figure 4 illustrates that cooling for electricity generation constitutes the dominant use of water (35%), followed by agriculture (29%) and public water supply (21%). The manufacturing sector also accounts for a substantial proportion (15%). In contrast, construction and mining and quarrying each represent only 1% of total abstraction. These patterns demonstrate the strong dependence of key economic sectors on water resources and highlight the urgent need to promote wastewater reuse, particularly in agriculture and public supply, especially in regions facing water scarcity.

While water abstraction has decreased in certain sectors, it has shown an upward trend since 2010 in areas such as agriculture (+3%), manufacturing (+4%) and domestic supply (+7%), highlighting the growing relevance of water in urban development, food production and industrial activities [34].

In this context, the reuse of treated wastewater emerges not only as a means of reducing pressure on freshwater bodies, but also as a sustainable solution to meet growing demands in irrigation, urban landscaping, industry and even indirect potable applications.

3.3. Emerging Contaminants and Microbial Risks in Reclaimed Water

The reuse of treated wastewater poses significant concerns for human health, primarily due to the potential occurrence of microbial pathogens and emerging contaminants. The World Health Organization (WHO) emphasizes that waterborne diseases caused by pathogens such as E. coli, Campylobacter, Shigella, Giardia, Cryptosporidium, norovirus, and hepatitis viruses remain a major public health risk [35]. Many of these pathogens have acquired antimicrobial resistance (AMR), complicating therapeutic options and heightening the risk of untreatable infections. Ensuring safe water is therefore essential not only to prevent disease transmission but also to limit antibiotic use and preserve their clinical efficacy.

WWTPs, although critical in safeguarding public health, face substantial challenges in the removal of pharmaceuticals, antibiotics, and antibiotic-resistant bacteria (ARB). Depending on the compound class and medical application, up to 80% of an administered antimicrobial dose can be excreted as active substance or metabolite, ultimately reaching WWTPs [36]. These facilities may function as reservoirs for ARB and antibiotic resistance genes (ARGs), thereby contributing to the dissemination of antimicrobial resistance within natural ecosystems. Furthermore, resistance can also originate from untreated animal excreta from livestock and aquaculture activities, which may reach soils and aquatic environments through practices such as manure application or surface runoff [37].

According to the EEA, AMR infections are responsible for around 35,000 deaths annually in the EU, Iceland and Norway [38]. These resistance genes have been detected in WWTPs’ effluents, freshwater systems and even in lakes. In response, recent legislative initiatives, including the revision of the Environmental Quality Standards Directive and the Groundwater Directive, seek to introduce thresholds for substances such as per- and polyfluoroalkyl Substances (PFAS), pharmaceuticals, pesticides, microplastics and AMR genes. These measures will be added to the official “watch list” once validated monitoring methodologies become available [27].

Moreover, the use of reclaimed water for irrigation has revealed additional risks. Empirical studies have confirmed the presence of pathogens such as E. coli, Salmonella, methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci in treated wastewater used in agriculture. Such conditions can promote the persistence of total and fecal coliforms in crops. According to the WHO, bacterial groups classified as ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) represent a major concern due to their resistance profiles and widespread prevalence in the food chain [39].

Many WWTPs across Europe were not originally designed to remove emerging contaminants or ARB [40]. Following human consumption, a substantial fraction of pharmaceuticals is excreted in active form. Evidence indicates that, depending on the compound, between 30 and 90% of the administered dose can enter sewage systems unaltered. While biological treatment can partially degrade certain substances, others—such as antibiotics and endocrine disruptors—remain largely intact, persisting in both treated effluents and residual sludge. This is particularly critical in countries where sewage sludge is applied to agricultural soils [41].

Quantitative risk assessments for pathogen and ARG dissemination through water reuse are crucial for public health. The WHO has modified water quality guidelines for reuse based on epidemiological studies, integrating microbial risk assessments to establish acceptable health standards [42]. Quantitative microbial risk assessment (QMRA) encompasses four key steps: hazard identification, exposure assessment, dose–response modeling, and risk characterization, which collectively inform the maximum acceptable risks for different water reuse scenarios [43]. Implementing QMRA provides a framework for evaluating health risks across various water conservation strategies, ensuring practices align with public health objectives [44,45].

To address these challenges, robust disinfection strategies must be adopted. Technologies such as chlorination, ozonation and ultraviolet (UV) radiation are commonly employed to inactivate pathogens in treated wastewater [46]. However, the effectiveness of any disinfection process is closely linked to upstream treatment quality; sufficient reduction in organic matter and suspended solids is essential to ensure pathogen removal and protect both human health and the environment [40].

3.4. Challenges in Current Wastewater Treatment

Conventional disinfection methods, primarily chlorination and UV radiation, remain the most widely used technologies in European WWTPs. Despite their widespread application, these methods have significant limitations. For instance, chlorination can lead to the formation of harmful by-products, some of which pose potential risks to human and environmental health. Similarly, while UV radiation is effective against many microorganisms, its efficacy is limited against resistant pathogens, and it often requires substantial energy input. Advanced treatment methods, such as ozonation, provide enhanced disinfection performance but come with the trade-off of higher operational costs and increased energy consumption, ranging from 10% to 60%, depending on system configuration and load [47].

According to the EEA, disinfection is currently applied to 31% of wastewater discharged into coastal waters or estuaries, and to 17% of inland discharges. The majority of wastewater discharges still rely on conventional technologies [47]. As illustrated in Figure 5, a significant proportion of EU Member States report either zero or very limited use of advanced disinfection methods, indicating uneven progress in addressing microbial safety.

In response to this, advanced oxidation processes (AOPs) have gained attention. AOPs generate highly reactive oxygen species (ROS), which can non-selectively degrade organic contaminants and inactive pathogens by attacking their cellular structure, nucleic acids and metabolic pathways. Unlike conventional methods, AOPs leave no harmful residues and offer higher efficacy against AMR-associated strains [40]. Several countries, including Spain, Switzerland, Germany and the Netherlands, have launched pilot initiatives or upgraded facilities to integrate AOPs into tertiary treatment systems.

Among emerging technologies, photocatalysis stands out as a promising method for water treatment. It utilizes light-activated catalysts to degrade pollutants, such as pharmaceuticals, pathogens, and organic compounds, without generating harmful by-products. This method offers several advantages: Energy efficiency, as photocatalysis can be powered by solar energy, reducing dependence on external power sources; Effective pollutant degradation, capable of breaking down a wide range of contaminants, including those resistant to traditional treatments; Minimal by-product formation, as opposed to chlorination, photocatalysis does not produce harmful disinfection by-products; and Adaptability, as photocatalytic systems can be customized to specific local conditions and integrated into existing treatment infrastructures. This is an emerging field, continuously evolving with the aim of finding more sustainable and cost-effective methods for water purification [48,49,50,51,52]. The adoption of photocatalytic systems aligns with the EU’s goals on energy efficiency, resource recovery and circular water management. Enhancing pathogen removal while reducing chemical and energy footprints, photocatalysis supports the dual objective of ensuring water safety and addressing water scarcity in a sustainable manner.

3.5. Wastewater Treatment and Reuse

As outlined in Section 3.2, the availability of freshwater across Europe is highly uneven, influenced by climatic conditions and transboundary water flows (external flows from other countries). Agriculture remains the largest water-consuming sector in Europe, accounting for about 40% of total consumption, followed by energy production (28%), mining and industry (18%), with the textile industry being one of the most water-consuming, and European households (12%) [31]. Most consumption is concentrated in Southern Europe, particularly in Spain and Italy, where water scarcity is more acute and crop irrigation is essential during drier months [53]. For example, in Spain, reclaimed water plays a key role in addressing water scarcity, especially in the southeast of the Iberian Peninsula. The reuse of treated water meets approximately 5.4% of total water demand, with water quality regulated under RD 1620/2007 [54], which mandates the installation or upgrading of tertiary treatment systems to ensure effluent quality appropriate for its end use. Many WWTPs originally lacked regeneration treatment, relying only on secondary treatment, which is insufficient due to high load of suspended solids. Therefore, tertiary treatments are essential for water reuse applications [18].

According to the EEA [55], approximately 7–8% of Europe’s agricultural land is irrigated, with this figure rising to 15% in Southern Europe, where 95% of the total irrigation volume is concentrated (Figure 6). Seasonal demand peaks between April and August, driven by reduced precipitation and increased evapotranspiration. The reuse of treated wastewater is a sustainable solution to relieve pressure on freshwater sources and meet increasing demands in irrigation, urban landscaping, industry, and indirect potable uses. Unlocking this potential requires supportive governance, targeted investments and the deployment of efficient treatment technologies.

Globally, only around 11% of treated wastewater is reused, while nearly 50% of untreated wastewater continues to be discharged directly into water bodies without any form of treatment. The untapped potential for wastewater reuse is estimated at around 320 billion cubic meters per year [20].

In the EU, the current reuse rate of urban wastewater remains modest (around 3%). Annually, only around 1 billion m³ of treated wastewater is reused, representing just 2.4% of the total treated effluent and less than 0.5% of total freshwater withdrawals. Countries such as Cyprus already reuse over 90% of their wastewater, followed by Greece, Malta, Portugal, Italy, and Spain (1–12%). Other countries, including Belgium, Germany, and Sweden, have adopted water reuse strategies for industrial use, aquifer recharge, and environmental protection [47].

The Water Framework Directive [22] sets the objective of achieving good chemical and quantitative status for all groundwater bodies and mandates that water abstraction must not compromise water body status. Recent data reveal that approximately 18% of groundwater bodies and 38% of surface bodies in the EU have failed to achieve good chemical status in 2022 [56,57]. This chemical degradation adds further pressure on freshwater resources, underscoring the need to advance water reuse practices as a means to protect water quality and reduce dependence on overexploited sources.

As of 2025, the EU operates over 20,000 UWWTPs, ensuring the effective collection and treatment of wastewater from towns and cities. The revised Urban Wastewater Treatment Directive (UWWTD), which will enter into force on 1 January 2025, builds upon previous efforts to improve water quality across Europe [58]. Although the new EU regulations for water reuse in agriculture do not yet establish pathogen-specific limits, they do mandate the monitoring of E. coli and the implementation of risk management plans to mitigate microbiological risks. In this regard, it is relevant to recall the requirements established by the UWWTD (Directive 91/271/EEC) [21], which mandates that agglomerations of more than 2000 p.e. must implement secondary treatment, and those above 10,000 p.e. must apply more stringent (tertiary) treatment, including nutrient removal. These obligations are now reinforced and expanded by the new Directive (EU) 2024/3019 [26], which introduces more ambitious targets for micropollutant removal and energy neutrality in large WWTPs by 2045, supporting the EU’s goals under the Green Deal and Zero Pollution Action Plan. Considering current treatment capacities across Member States, WWTPs serving more than 10,000 p.e. should be the primary targets for upgrading to meet advanced treatment standards, especially in regions still relying on primary or secondary stages.

As an example, and according to national data from 2024, Spain had a population of 47,907,370 inhabitants and 2059 wastewater agglomerations serving more than 2000 p.e. These agglomerations generated a total load of 64,535,402 p.e., of which 99% was connected to urban collecting systems, while the remaining 1% was served by individual or alternative systems (IAS), such as septic tanks or micro-stations. These agglomerations are treated by 30 primary, 566 secondary, and 1023 more advanced treatment plants, with a total design capacity of 99,794,323 p.e. In terms of water reuse, Spain currently reclaims approximately 400 hm³ per year of treated water, 12% of which is reused for industrial applications, primarily sourced from municipal effluents [20].

Despite the high levels of connectivity across Europe, where 21,626 WWTPs collect and treat wastewater from approximately 538.4 million people in the EU-27 [59], around 5% of the EU population remained unconnected to any wastewater collection network in 2021. These WWTPs operate under the framework established by the UWWTD [21], which sets requirements for the collection, treatment, and discharge of urban wastewater to protect the environment.

Nevertheless, connection and treatment infrastructure alone do not guarantee good ecological outcomes. Although 85% of permitted WWTPs in the EU apply at least secondary treatment and overall connection rates reach 81% [60], only 42% of European rivers and streams currently meet the “good” ecological status required under the Water Framework Directive [61]. This discrepancy points to persistent pollution challenges, particularly related to chemical contaminants.

Indeed, recent data from the EEA’s Zero Pollution Dashboard show that only 31% of surface water bodies achieve “good” chemical status, while 23% of groundwater bodies are in poor chemical condition (Figure 7). The accompanying map of river basin districts illustrates the widespread presence of ubiquitous, persistent, bioaccumulative and toxic substances (uPBTs), including mercury and brominated flame retardants. These pollutants are detected even in countries with robust wastewater treatment systems, underscoring the need for integrated management approaches [60]. As an example of national strategies, such as Switzerland’s WWTP upgrades, aim to enhance microbiological water quality to ensure safe irrigation. These upgrades are particularly important in the context of projected reductions in rainfall and longer growing seasons due to climate change [47].

This context highlights a dual challenge: improving microbiological quality through advanced pathogen removal, as addressed in previous sections, while also implementing targeted measures to control chemical contamination. These may include enhanced monitoring programs, stricter source control regulations and the adoption of advanced purification technologies capable of addressing emerging pollutants and legacy contaminants.

3.6. Regional Analysis of Treated and Reclaimed Wastewater

In light of these pressures, treated wastewater reuse emerges as a strategic necessity, particularly in regions with limited freshwater availability. Reuse can reduce abstraction from rivers and aquifers, enhance water supply reliability during droughts, and help adapt to climate change by making water use more circular and efficient [27].

There are progressive levels of treatment that urban wastewater can undergo in wastewater treatment plants. Conventional primary wastewater treatment mainly removes suspended solids, while the second level treats nutrients, pathogens and some chemicals. The tertiary level is more tailored to the specific case. Since the UWWT Directive [21] was implemented, the proportion of the population connected to wastewater treatment has been steadily increasing. As a result, by 2022, 81% of the EU population was connected to wastewater treatment at the secondary level at least [62].

The data presented in this section have been obtained from Eurostat, specifically from the dataset on the population connected to wastewater treatment plants [63], with the most recent update corresponding to the year 2021. For analytical purposes, results have been grouped by European regions (Northern, Central, Southern, Eastern and South-Eastern).

The level of treatment received by the population is classified into four categories: not connected to an urban and other wastewater treatment plants (NC), connected to primary treatment (PT), secondary treatment (ST) and tertiary treatment (TT). These categories follow the definitions established by the EEA: PT refers to mechanical treatments aimed at removing suspended solids; ST involves the reduction in dissolved and suspended organic matter, including biological methods and TT includes nutrient removal and typically involves a disinfection process. The NC category refers to populations whose wastewater is not connected to a centralized system and may be treated independently or discharged without centralized treatment.

The following presents the results after analyzing and classifying the data. Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12 illustrate a regional breakdown, providing a comparative overview of the extent and level of wastewater treatment across different European regions, highlighting both disparities and progress in complying with EU directives.

Northern countries. The countries in this region are Finland, Iceland, Norway, and Sweden. On average, 100% of the population in this area is connected to WWTPs, with the vast majority receiving advanced treatment. Tertiary treatment accounts for approximately 75% of all treatments, while primary treatment represents around 9%. Only Norway reports secondary treatment data, with 26% of the population receiving this level of treatment. The non-connected population is minimal, averaging just 0.5%.

Central countries. This region consists of Austria, Belgium, Denmark, Germany, Luxembourg, the Netherlands, Switzerland, and the United Kingdom. On average, 99% of the population in these countries is connected to a WWTP. Among the connected population, 80% receive tertiary treatment, 9% receive secondary treatment, and primary treatment accounts for less than 1%. The proportion of the population not connected to treatment facilities is low, averaging 0.8%.

Southern countries. These countries are Cyprus, France, Greece, Italy, Malta, Portugal and Spain. On average, 96% of the population in this area is connected to a WWTP. The distribution of treatment levels shows a predominance of tertiary treatment (54%), followed by primary (18%) and secondary (13%), while almost 2% is discharged without treatment. Spain shows the highest proportion of tertiary treatments (57%), while Malta stands out for relying mostly on primary treatment (91%) and a lack of secondary (7%) or tertiary (0%).

Eastern countries. This area is composed of the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia. On average, 87% of the population in these countries is connected to WWTPs. The connection is primarily to secondary and tertiary treatment systems, with about 20% of the population receiving secondary treatment and 57% tertiary treatment. Primary treatments are nearly negligible across the region (0.16%) and the share of the population not connected to WWTPs remains low, averaging 0.7%.

South-eastern countries. Albania, Bulgaria, Croatia, Romania, Serbia and Turkey are the countries in this zone. This region shows the lowest average connection to WWTPs in Europe (around 60%) with significant disparities between countries. Albania and Serbia stand out with very low connectivity rates (26% and 16%, respectively), while Bulgaria and Croatia are above 90%. On average, 19% of the population is not connected to any treatment systems. Regarding treatment levels, the mean distribution is 6.7% for primary treatment, 15% for secondary and only 26% for tertiary treatment, indicating limited capacity for advanced wastewater purification.

The results of the analysis conclude that across the European Union, significant disparities persist regarding both connectivity to WWTPs and the treatment level applied. Central and Northern Europe maintain near-universal connection rates, with a strong predominance of tertiary treatment, particularly in countries such as Austria, the Netherlands, Finland and Sweden. In contrast, Southern, Eastern and South-Eastern Europe display more heterogeneity. While some countries like Spain, France and the Czech Republic exhibit substantial tertiary coverage, others, such as Malta, Albania and Serbia, still rely primarily on primary treatment or have large portions of their population unconnected to any wastewater treatment. Notably, the Balkans and parts of South-Eastern Europe show the lowest connectivity and highest non-treatment rates. In this context, enhancing secondary and especially tertiary treatment infrastructure remains essential to align with the EU’s increasingly stringent water reuse and environmental protection standards. Improving these treatment levels will be crucial not only for achieving compliance, but also for ensuring microbiological safety, particularly with respect to indicators like E. coli in reclaimed water.

Over the past decades, the implementation of wastewater treatment infrastructure across Europe has shown heterogeneous progress. Based on Eurostat data averaged from 2000 to 2022, Central Europe leads with an average of 89% of its population connected to WWTPs at least in secondary treatment, followed by Eastern Europe (67%), Northern Europe (58.6%) and Southern Europe (58%). South-Eastern Europe shows the lowest connectivity, with only 32% of the population connected to WWTPs on average. These improvements have played a critical role in reducing nutrient loads and organic pollutants discharged into receiving waters. However, many WWTPs still lack the capacity to meet the new quality requirements for water reuse, particularly regarding microbiological criteria. Therefore, facilities already operating with tertiary treatment should be considered key candidates for further upgrades, such as the integration of disinfection systems or advanced tertiary processes to enhance removal efficiency of pathogens and emerging contaminants, in line with the objectives of Regulations (EU) 2020/741 [23].

3.7. Estimation of the Potential Market

The results from the analysis of the previous sections are conclusive in that, despite the high levels of connectivity to WWTPs across Europe, treated effluents remain significantly underutilized as a resource. Globally, around 380 billion m³ of municipal wastewater are produced annually, with projections indicating a 24% increase by 2030 and a 51% increase by 2050. Yet, wastewater is still primarily perceived as a pollutant to be disposed of, rather than as a strategic source of water, energy, and nutrients. This underuse reflects a missed opportunity to address water scarcity and enhance climate resilience through circular water management [64].

As indicated in Section 3.5, in the EU, approximately 40,000 million m³ of wastewater were treated annually in 2023. However, only 1100 million m³ (2.4%) of treated effluents and less than 0.5% of freshwater withdrawals were reused [65]. Although some studies estimate that this volume could increase sixfold, reaching up to 6 billion m³ per year [20], it is already regarded as a significant opportunity for investment in advanced wastewater reuse technologies.

To conduct a more accurate assessment of the reclaimed water market niche in Europe, a study was carried out using data from a recent European Commission report, specifically the WISE Freshwater Platform [66]. The annual volumes of wastewater generated per country were estimated using daily wastewater production data reported by the WISE Freshwater Platform. These national profiles provide estimates of the total wastewater volume in million cubic meters per day (million m³/day), accounting for both households and selected industries within urban agglomerations. For each country, the daily wastewater volume was multiplied by 365 days to derive the total annual volume, expressed in million cubic meters per year (million m³/year), as presented in

Table 2. Wastewater treated (effluent) in the European WWTPs.

Country	m3/y	Country	m3/y
Austria	1.526 × 109	Italy	5.694 × 109
Belgium	6.716 × 108	Latvia	1.095 × 108
Bulgaria	4.891 × 108	Lithuania	1.898 × 108
Croatia	3.395 × 108	Luxembourg	4.745 × 107
Cyprus	7.665 × 107	Malta	4.745 × 107
Czech Republic	6.789 × 108	Netherland	1.445 × 109
Denmark	8.797 × 108	Norway	5.877 × 108
Estonia	1.095 × 108	Poland	2.716 × 109
Finland	4.052 × 108	Portugal	9.527 × 108
France	5.347 × 109	Romania	1.448 × 109
Germany	8.023 × 109	Slovakia	2.957 × 108
Greece	8.697 × 108	Slovenia	1.168 × 108
Hungary	9.089 × 108	Spain	4.606 × 109
Ireland	3.760 × 108	Sweden	9.344 × 108

. This approach assumes constant daily generation throughout the year and does not account for seasonal variations or losses due to reuse.

As illustrated by the estimated annual volumes of wastewater produced across European countries, the potential for water reuse is substantial. Reclaimed water constitutes a reliable yet underutilized resource that can play a significant role in addressing water scarcity and strengthening climate resilience. In contrast to conventional freshwater sources, treated wastewater is less affected by seasonal droughts and hydrological variability, making it a strategic option for ensuring supply during peak demand periods, particularly in agriculture. Furthermore, its use supports the protection of sensitive ecosystems by alleviating abstraction pressures on natural water bodies and by facilitating the removal of pathogens and emerging contaminants that would otherwise enter the environment. Maximizing wastewater reuse therefore not only advances the objectives of the European Green Deal and the Circular Economy Action Plan, but also delivers tangible social, economic, and environmental benefits at both local and regional scales.

Countries such as Cyprus and Malta already reuse 90% and 60% of their wastewater, respectively. In the Southern EU, Spain, Italy and Greece reuse between 5% and 12% of effluents. Meanwhile, countries like Belgium, Germany and the UK apply reclaimed water for industrial use, aquifer recharge and urban purposes [20].

Technological innovations in wastewater recycling and technological advancements in wastewater treatment have made it possible to recycle wastewater to a high standard that meets the safety requirements for both agricultural irrigation and potable use. Technologies such as membrane filtration, biological treatment processes, advanced oxidation processes and nanotechnology have all contributed to making recycled water safer, cleaner and more efficient.

Recycling wastewater provides environmental benefits that extend beyond water savings. By reducing the discharge of untreated effluents into natural water bodies, recycled water helps preserve aquatic ecosystems and minimize pollution. The use of treated wastewater for agricultural irrigation can also prevent the overexploitation of saline or untreated sources, which frequently result in soil degradation, salinization, and land erosion. Furthermore, wastewater recycling reduces the environmental footprint of water management, fostering a more sustainable and eco-friendly approach to resource use. European countries could establish a global benchmark for sustainable and efficient water solutions as global water challenges intensify, thereby contributing to the achievement of the United Nations Sustainable Development Goals (SDGs), particularly SDG 2 (Zero Hunger) and SDG 6 (Clean Water and Sanitation) [67].

In this context, countries such as Spain, Germany, the Netherlands, and the United Kingdom serve as reference models for wastewater reuse. Spain, in particular, employs tertiary-treated water to irrigate high-value crops in arid regions such as Andalusia, Murcia, and Valencia, often through public–private partnerships. Germany integrates reuse in industrial applications, while the Netherlands has pioneered closed-loop systems to minimize water loss. The United Kingdom has advanced indirect potable reuse, further expanding the strategic value of treated wastewater [67].

4. Conclusions

This study frames the growing relevance of wastewater treatment and reuse within the broader context of water scarcity, environmental degradation and rising regulatory demands across Europe. Rather than viewing wastewater as a waste stream, the focus is increasingly shifting toward its potential as a valuable resource. From this premise, the document explores the technological and regulatory landscape surrounding advanced treatment solutions. Drawing on data from Eurostat, the European Environment Agency and recent legislative updates, the report provides a regional analysis of wastewater generation, treatment levels and reuse practices. This progression aims to offer a coherent narrative that highlights both the need and potential for innovation in the European water sector.

At the strategic level, the data confirms the existence of a substantial opportunity for Europe to combat water scarcity through an innovative water recovery solution. Despite high levels of wastewater collection and treatment, reuse rates remain limited and uneven across Member States. Enhancing reclamation capacities using scalable and regulation-compliant technologies could significantly increase the availability of non-conventional water sources, particularly for agriculture and industry. Scaling advanced, regulation-compliant reuse—paired with transparent risk communication, public engagement, and rigorous monitoring—can deliver co-benefits for ecosystem protection, climate resilience, and food and water security. Embedding reuse within coherent governance and finance frameworks is likely to yield measurable planetary-health gains while safeguarding public health. As climate change intensifies drought conditions and increases water demand, wastewater reuse could become a key pillar in achieving the goals of the European Green Deal, the Circular Economy Action Plan and the United Nations Sustainable Development Goals (SDG 6 and SDG 2).

The reclaimed water sector offers considerable promise in tackling global water challenges, with a growing market bolstered by economic, technological, and regulatory advancements. The industry’s future will depend on overcoming existing barriers related to health risks, public perception, and environmental sustainability, all of which collectively influence the trajectory of reclaimed water’s adoption across different regions and sectors.