Applications for Non-Conventional Water Resources in the Mediterranean Basin: A Literature Review

Abstract

We conducted a systematic review of peer-reviewed scientific bibliography published between 2010 and 2023, concerning the exploitation of Non-Conventional Water Resources (NCWR) in the Mediterranean Basin. The goal was to enhance our understanding of NCWR uses, reveal knowledge gaps, and identify future trends, risks, and challenges. The methodology comprised the inclusion, mining, filtering, and grouping of key elements retrieved from the surveyed items, followed by the deciphering of their intra-cluster variability and the links between them. Of the 978 publications harvested from the SCOPUS pool, 193 were eventually selected to form the NCWR database. The latter extends to 282 entries, each for an individual, i.e., single method and study area, application, compiled by 24 attributes per registry. The study provides insight on (i) the technologies most frequently implemented, (ii) the geographical distribution and spatial scale of the applications, (iii) their temporal trends, (iv) their objectives, (v) their relationship with nature and society. The work aims to fuel the discussion on improving policy-making, resource management, and adaptation to the climate crisis.

1. Introduction

Water is a renewable natural resource, but it is of limited availability. It covers almost 71% of the Earth’s surface, yet circa 96.5% of its total volume is saline (ocean water). The vast amount of the remaining freshwater—approximately 2.1%—is tied in icecaps, glaciers, the atmosphere, and the soil, leaving only 0.7% for human exploitation [1,2]. The already limited availability is challenged today by the rapid growth of the global population [3,4] and the rising living standards. It is noteworthy that water use in the 20th century grew at more than twice the rate of demographic increase [5]. The high demand for drinking water, food, and fiber production is dramatically intensifying the pressure on water reserves, infrastructure, and farming systems. The problem is exacerbated by the adverse effects of the climate crisis, especially in the arid and semi-arid regions of the world [6,7]. It is estimated that by 2050, around 2 B people globally will be affected by water scarcity [8].

Irrigated agriculture is a frontrunner in global water demands, responsible for 70% [9] to 80% [10] of freshwater consumption on average, and 40–43% of groundwater (GW) withdrawals [11]. Despite being practiced in only 20% of the total arable land worldwide [12], it contributes 40% of global food production. With Earth’s population expected to reach 9.7 B in 2050, irrigated land will have to expand by approximately 32 M hectares—with a subsequent increase of water demand by 11% [13]—to satisfy the growing need for food and other services.

The Mediterranean Basin (also found in the bibliography as Mediterranean Region; differentiates from the respective hydrological watershed that extends further into the mainland) is characterized by acute water scarcity. It is inhabited by more than 50% of the world’s water-poor population, comprising only 3% of the global freshwater resources [14]. Moreover, the Region constitutes a hotspot concerning the climate crisis implications [15,16,17,18]. Changes in the patterns of rainfall [19], temperature [20], drought [21], recharge [22], and runoff [23] point to a future of low water availability, frequent extreme events, and high variability between the dry and the wet season [24,25,26]. These trends are expected to aggravate, increasing the hydrological pressure on an already highly stressed region [27]. Agriculture is expected to pose the hardest pressure among sectors. Drought intensity and the renewable water resources decrease per capita—from 2300 to 1800 m³ between 1990 and 2015 [27] in southern Europe—has already caused crop yield reductions [28] with severe financial consequences [29].

At the macro-regional level, the Mediterranean Basin exhibits significant hydrological imbalances. Many countries in the region experience chronic water deficits, with average annual renewable water resources per capita falling well below the water scarcity threshold of 1700 m³ y⁻¹. For instance, countries such as Malta, Cyprus, and Israel register values under 500 m³ y⁻¹, classifying them as severely water-stressed [30]. Recent assessments indicate that more than half of Mediterranean countries face annual water deficits, especially during the summer months, due to mismatched supply-demand cycles and seasonal precipitation patterns [31]. The average annual water deficit in southern Mediterranean countries (e.g., Morocco, Tunisia, Egypt) ranges between 2 and 5 B m³, leading to over-reliance on groundwater abstraction and inter-basin transfers. This situation is compounded by weak enforcement of water governance policies and high non-revenue water rates in urban networks [32]. As such, the region’s water policy landscape is marked by a fragmented yet evolving framework, wherein EU member states adopt directives like the Water Framework Directive [33], while southern neighbors pursue national strategies, often under donor-supported programs.

In this water-scarce environment, Mediterranean countries are obliged to provide access to water in sufficient quantity and good quality to their citizens. To cover demand, the supplemental use of Non-Conventional Water Resources (NCWR) for crop irrigation emerged as a pragmatic alternative to modern water infrastructure and management challenges, within the context of Integrated Water Resources Management (WRM) [34]. The objective is to (i) equilibrate supply and demand, preventing the long-foreseen deficit crisis, (ii) sustain (or increase) farmland productivity, (iii) balance the needs of competing uses, i.e., agricultural, domestic, industrial—in other words, avert conflicts through equitable allocation [35,36], (iv) address the spatiotemporal variation between supply and demand [37], (v) reduce incompatibility between market-driven agriculture and (agro) ecological goals, (vi) tackle climate uncertainty by ensuring climate-independent water use, (vii) revert the declining quality of water bodies, and (viii) conciliate social considerations, guarantee food security and economic stability [38,39]. In urban environments, NCWR aid conventional systems to cope with the rising demand due to population growth and tourism increase [40], and underpin the adaptation of drainage networks to urban sprawl [41]. After all, modern water policy marks the shift from a supply-oriented to a demand-management approach [42]. In other words, instead of modifying natural processes, it aims to alter human and social behaviour towards this resource.

In this context, several adaptation strategies and legislation frameworks have been introduced. Indicatively, the European Union (EU) Urban Wastewater Treatment Directive [43], the EU Water Framework Directive [33], the World Health Organization (WHO) Guidelines for the safe use of wastewater (WW), excreta and greywater in agriculture and aquaculture [44], the EU Blueprint to safeguard Europe’s water resources [45], the United Nations (UN) Sustainable Development Goals (SDGs) and specifically objectives No. 6 ‘clean water and sanitation’ and No. 11 ‘sustainable cities and communities’ [46,47], etc. As to the treatment and application of NCWR in agriculture, Regulation 2020/741 (https://eurlex.europa.eu/eli/reg/2020/741/oj, accessed on 30 April 2025) is already in force, becoming obligatory for all Member States (MS). Included in the Circular Economy Action Plan (https://environment.ec.europa.eu/strategy/circular-economy-action-plan_en, accessed on 30 April 2025), this ambitious innovative framework aims to foster the transition towards a greener circular model [48], stimulating in parallel societal acceptance of NCWR use for crop irrigation [49].

The study conducted an in-depth review of scientific peer-reviewed literature about the valorization of NCWR technologies in the Mediterranean Basin (See Supplementary Material). Despite the extensive bibliography available, essential questions needed to be answered to enhance our understanding of NCWR uses in this region. Specifically, what is the geographical distribution and spatial scale of the applications? Which technologies are most frequently implemented and why? What are their aims? Temporal trends? Relations with the natural environment and the socioeconomic framework? To this end, this analysis aimed to map NCWR use considering their strengths and weaknesses, reveal knowledge gaps, summarize key findings, provide insights on past and contemporary efforts, and identify future trends and challenges. The goal is to support socioeconomic research on water scarcity—driven by population growth, intensive agricultural practices, and climate variability—and evaluate water resilience attempts.

2. Materials and Methods

2.1. Study Area

The study area is the Mediterranean Basin. This broad geographical space comprises the lands that surround the Mediterranean Sea, experience Mediterranean climate (i.e., warm (to hot) dry summers; mild (to cool) rainy winters [50,51], and support distinct Mediterranean ecosystems [52]). The Basin occupies portions of three continents (Europe, Africa, and Asia), and 23 countries (not exclusively; depending on the view). To the north is delimited by those of the southern European coast, namely (from west to east) Portugal, Spain, France, Italy, Monaco, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania, Greece, Malta, and Cyprus, to the south by those of the northern African coast, namely (from west to east) Morocco, Algeria, Tunisia, Libya, and Egypt, and to the east by those of the western Asian coast, namely (from north to south) Turkey, Syria, Lebanon, Palestine, and Israel (Figure 1). Portugal and the Canary Islands (a Spanish autonomous community and archipelago complex in the Atlantic Ocean) are included in the study without ‘bordering’ the Mediterranean, given common economic, geopolitical, historical, ethnic, and cultural characteristics.

2.2. Inclusion Criteria

The study focused on specific technologies and methods conventionally applied for the valorization of NCWR, namely Managed Aquifer Recharge (MAR), Rainwater Harvesting (RWH), WW Reuse (WWR), and Desalination. This section outlines the four approaches considered.

It is underlined that in the Mediterranean Basin there is relatively high use of natural saline water, which often requires dilution with freshwater (or, in cases, α different type of desalination from that applied to seawater) and fitting to the appropriate crop (or even breeding for tolerant crops). Given the marginal character of these applications, it was decided not to include them in this review.

2.2.1. Managed Aquifer Recharge (MAR)

GW is very important for human development, being the largest source (~97%) of fresh water on Earth. It is the main ‘supplier’ of irrigated agriculture and a critical source of potable water in arid and semi-arid regions, especially in dry periods. Its exploitation increased alarmingly by the second half of the 20th century, due to population growth, the rising living standards, the shift in climate patterns, i.e., intensity and frequency of droughts [53,54], the technological progress in GW exploration and drilling, and the overall economic development [55]. Systematic mismanagement has aggravated the pressure on GW systems, especially coastal (mainland, insular) aquifers. The excessive use of pesticides and fertilizers on farmlands led to water pollution, and the overuse of storage depletion and water level drop (hydraulic barrier retreat), causing seawater intrusion and salinization [56,57,58,59,60,61].

MAR is a widespread artificial method for the rehabilitation of underground basins [62,63]. This human-induced (controlled, measurable) replenishment process can improve water quality, tackle brackish water encroachment, restore hydrological balance, transcend natural supply gaps (seasonality, trends), and increase availability for future use. Recharge is achieved through infiltration ponds, percolation tanks, and injection wells [64], using treated WW [65,66] or excess fresh water. Overall, MAR constitutes a robust [67,68,69], socially accepted [63], cost-efficient [70] method to counteract the effects of climate uncertainty [54,71,72,73] and unsustainable GW management [74,75].

2.2.2. Rainwater Harvesting (RWH)

Small-scale RWH (dams excluded) is an ancient technique, long implemented in the Mediterranean Basin [76,77,78,79,80,81]. RWH aims to (i) provide access to a natural resource with minimum cost, (ii) address water shortages, (iii) decrease dependency on costly and complex distant water transfers that require investments in infrastructure (dams, river regulation, energy networks) and the nexus’ management, (iv) reduce non-point source pollution [82,83]—by extension treatment costs, (v) mitigate the stress on ground and surface water reserves, (vi) reduce flood risk (exacerbated at urban lands by soil sealing) and alleviate pressure off the drainage network. Aquifer recharge, reduced erosion rates, runoff control, soil moisture preservation, increased water storage capacity, and yield improvement [84,85,86,87] are additional benefits of water conservation on farmlands, after the installation of check dams, terraces, contour strips, etc. [88].

During the 20th century, changes in socioeconomic dynamics, the greater availability and guaranteed (regular) supply of water, urbanization, and the modernization of agriculture led to the gradual abandonment of traditional collection practices. In recent years, however, RWH has (re)gained momentum. Contemporary eco-friendly systems, also known as Sustainable Urban Drainage Systems (SUDS) [89], are at the forefront of this changing process. SUDS are designed to replicate (and restore, when possible) the natural hydrological cycle at the micro-scale, in a simple, flexible, and cost-competitive manner. Distributed elements such as green roofs [90,91], permeable surfaces [92], and constructed wetlands are only some of their structural features. SUDS swiftly convey stormwater to the nearest recipient, either to be discharged (by drainage canals, water bodies) or stored (in small-scale reservoirs, cisterns, domestic tanks) for future use [93]. By controlling runoff close to the source [94,95], the sewage network receives lower volumes and decreased peak flows [96,97] and can attenuate floods more effectively [98]. Attached to the centralized infrastructure nexus, they complement water filtering, evaporation, infiltration/aquifer replenishment [99]. Furthermore, rainwater is considered a rather ‘clean product’ in terms of quality and treatment requirements [100,101]. Thus, it is appropriate for non-potable uses such as washing of cars and outdoor surfaces, irrigation of gardens and sports facilities, toilet flushing, laundry, etc. [102]. After all, climate crisis adaptation is achieved [103] through water scarcity resilience [104] and energy saving/carbon emission reduction [105,106].

2.2.3. Wastewater Reuse (WWR)

Numerous studies across Europe [107,108] and the Mediterranean [109,110,111,112] have highlighted the importance of reusing treated domestic WW in agriculture. Indicative benefits are the reservation of high-quality fresh water for drinking purposes [36], low investment costs and energy requirements, low dependency on seasonal variations and climate trends (droughts), food security (self-efficient food production), market price stability, reduced cultivation costs (lower fertilization needs), creation of green jobs [113] and environmental protection. The latter can be summarized in reduced disposal of polluting effluents into surface water bodies [114,115], limited use of fertilizers due to the richness of the reclaimed water in nutrients and organic matter [109,116], reduced treatment cost, and effective effluent depuration by applying the recycled WW to soil [114,117].

Tunisia and Israel display the best recycling performance among Mediterranean countries. They reuse 4.3% and 15% of their available water resources, respectively, with a significant mean annual increase ratio. The notably lower annual amount in the EU MS of the Region, i.e., merely 2.4% of the treated urban effluents, is ascribed to the comparably lower water stress (hence urgency) they are experiencing, and barriers of social (lack of NCWR literacy, high quality standards perception, health concerns), scientific (rather limited consensus regarding the impacts/hazards during the processing and application), financial (implementation cost), and legal (policy gaps, governance limitations, strict legislation) nature. The EU aims to increase water reuse by ~300% (from 1.7 to 6.6 B m³ y⁻¹) and reduce freshwater consumption by 5% [118].

2.2.4. Desalination

Desalination is based on the removal of dissolved salts and minerals from saline seawater (58.9%) and brackish GW (21.2%) [119] and is primarily applied in arid coastal areas [120] and islands [121,122]. Desalination can extend supply way beyond the availability of the water cycle [123], whereas reclaimed water is limited by domestic WW production and brackish GW by the aquifer’s capacity. By manipulating an apparently limitless ‘capital’, it can effectively transcend climatological and hydrological constraints of continental water resources, providing a high-quality ‘product’ at unwavering rates to alleviate water shortage [124]. Additionally, desalinated seawater (DSW) circumvents social opposition and conflicts about long-distance water transfers [125,126,127], merits increased resilience to the climate crisis [128,129], and reduced chemical treatment for sanitation (hence ecological footprint; costs), etc. Besides, DSW is being strongly considered for irrigation agriculture [130,131,132]. Currently, however, the comparably higher cost to conventional resources and brackish GW desalination [133] limits its applicability only as a supplemental source, or for use on high-return crops [134]. This trend is soon expected to extend, even intensify, given the technological advancements and the progressive cost reduction.

Desalination is a relatively new technology for producing water, with the first large-scale plants being built in the 1960s (http://idadesal.org/desalination-101/desalination-by-the-numbers/, accessed on 18 January 2025). Yet in 2015, around 20,000 desalination plants were operating in 150 countries, delivering ~87 M m³ d⁻¹ of freshwater to more than 300 M people. This capacity is increasing annually by 7% on average [135], having reached ~97.2 M m³ d⁻¹ in 2019 [136]. The main reason for this rapid expansion is the advances in the Reverse Osmosis (RO) technology [137]. The new RO units have reduced the processing cost, hence the market value of DSW, by being simple, commercially available [138], and energy-efficient compared to their thermal alternatives [139,140]. This is why RO is considered the most adaptable technology for agricultural use [141,142].

2.3. Data Collection and NCWR Database Compilation

The dataset is compiled from peer-reviewed publications about the use of NCWR in the Mediterranean Region. The topic features in evaluated scientific journals, books, and conference proceedings that appear in Elsevier’s SCOPUS database (DB) (https://www.scopus.com/). The SCOPUS search engine was selected for being a powerful tool that provides (a) complete and consistent indexing records from a large pool of peer-reviewed publications [143,144], and (b) preliminary analysis of results based on bibliometric indicators: documents by year; per year by source; author; affiliation; country/territory; type; subject area; sponsor. Besides, SCOPUS may have a greater coverage of subjects included in the field of Earth and Atmospheric Sciences compared to other databases such as Thomson Reuters’ Web of Science (WOS) [145,146].

The methodology followed a cascade approach, comprising Text Mining (TM) and Performance-Intellectual Analysis (PeIA) [147,148] (In this study, the intellectual structure of the research field (collaboration networks, linkages between publications, etc.) was not investigated). TM is used for identifying scientific patterns, through (i) data retrieval—by setting a general inclusion criterion, i.e., the subject of interest, (ii) bibliometric data collection—by setting specific inclusion criteria, i.e., keywords, time periods, and (iii) semantics processing—by refining the inclusion criteria to avoid duplicate registries, bias due to spelling and typographical errors [149], etc. PeIA is used for pattern verification, through (i) data analysis and visualization, and (ii) conclusion drawing.

To cover the broad spectrum of NCWR applications regarding the study’s goals, several queries comprising keywords and syntax variants (Boolean strings) were initially built, in compliance with the SCOPUS nomenclature. Eventually, the search was narrowed down to the following criteria: TITLE-ABS-KEY surveys (i) non AND conventional AND water AND Mediterranean, (ii) runoff AND water AND harvesting AND Mediterranean, (iii) desalination AND Mediterranean, (iv) managed AND aquifer AND recharge AND Mediterranean, (v) wastewater AND reuse AND Mediterranean, (vi) water AND harvesting AND Mediterranean. The data used in the study are available at SCOPUS via https://www.scopus.com/ (accessed on 25 February 2025) with the Open Data Licensing Policy (

Table 1. Number of records per query between 2010 and 2023 (duplicate records included in all fields).

Query	Query (Verbal)	Retrieved	Included	Excluded	Not Found	Not in English
I 1	non AND conventional AND water AND Mediterranean	111	26 (23.4%)	69 (62.2%)	13 (11.7%)	3 (2.7%)
II 2	runoff AND water AND harvesting AND Mediterranean	49	27 (55.1%)	18 (36.7%)	4 (8.2%)	–
III 3	desalination AND Mediterranean	292	45 (15.4%)	185 (63.4%)	48 (16.4%)	14 (4.8%)
IV 4	managed AND aquifer AND recharge AND Mediterranean	30	13 (43.3%)	10 (33.5%)	3 (10.0%)	4 (13.3%)
V 5	wastewater AND reuse AND Mediterranean	200	81 (40.5%)	83 (41.5%)	34 (17.0%)	2 (1.0%)
VI 6	water AND harvesting AND Mediterranean	296	56 (18.9%)	204 (68.9%)	34 (11.5%)	2 (0.7%)

¹ URL: https://www.scopus.com/results/savedList.uri?sort=plfdt-f&listId=60823415&listTypeValue=Docs&src=s&imp=t&sid=5a615e23afe3856805f3f4ccb8cacc92&sot=sl&sdt=sl&sl=0&origin=savedlist&txGid=d8e427aaf298121b76fd863274f69f7b, accessed on 25 January 2025; ² URL: https://www.scopus.com/results/savedList.uri?sort=plfdt-f&listId=60823430&listTypeValue=Docs&src=s&imp=t&sid=27d0e2dd6ff857b64d9136959dd220e8&sot=sl&sdt=sl&sl=0&origin=savedlist&txGid=1a2943b0127d84ba253b46f04e6c4176, accessed on 25 January 2025; ³ URL: https://www.scopus.com/results/savedList.uri?sort=plfdt-f&listId=60823453&listTypeValue=Docs&src=s&imp=t&sid=13e8706c001e1f0a8b09cc0087ccf9eb&sot=sl&sdt=sl&sl=0&origin=savedlist&txGid=3468dd27e0cd464ffbf8b96aff1fc74d, accessed on 25 January 2025; ⁴ URL: https://www.scopus.com/results/savedList.uri?sort=plfdt-f&listId=60823462&listTypeValue=Docs&src=s&imp=t&sid=ef75e8a68a37bb2c47ec6de3dbc087b0&sot=sl&sdt=sl&sl=0&origin=savedlist&txGid=d7b7d5816e52eef70f21343bf647bff3, accessed on 25 January 2025; ⁵ URL: https://www.scopus.com/results/savedList.uri?sort=plfdt-f&listId=60823473&listTypeValue=Docs&src=s&imp=t&sid=c64d29707149c29cafb8d1fade2a085c&sot=sl&sdt=sl&sl=0&origin=savedlist&txGid=9da352df45b534a9b47256808f3d5925, accessed on 25 January 2025; ⁶ URL: https://www.scopus.com/results/savedList.uri?sort=plfdt-f&listId=60823480&listTypeValue=Docs&src=s&imp=t&sid=a3f3bb723d41c23a5b8a90b186ca1b7e&sot=sl&sdt=sl&sl=0&origin=savedlist&txGid=b5d75a00fdcb9b67cf3028b68112f906, accessed on 25 January 2025.

, footnote).

For the period 1 January 2010–30 April 2023, the queries generated 111, 49, 292, 30, 200, 296 records, respectively (Table 1). All accessible articles were downloaded, and the TM was completed with the exclusion (filtering) of those (a) not relevant to the study’s objectives, i.e., description/refinement of NCWR technologies and frameworks without practical application, conceptual/not spatially explicit research, research conducted in a non-Mediterranean country, (b) written in national language and not in English, (c) categorized as grey literature, i.e., conference abstracts, government publications, scientific reports, and (d) duplicates retrieved across surveys. Eventually, 193 contributions were selected, apportioned as query (i) → 26, query (ii) → 27, query (iii) → 36, query (iv) → 13, query (v) → 66, query (vi) → 25. The 198 suitable articles represent 282 entries in the NCWR DB, each for an individual (single method; study area) application, compiled by 24 attributes per registry. The information listed in

Table 2. Fields of the NCWR DB.

	Cluster	Entry	Data Type	Options
I	Record Information	Query	Open (alphanumeric)
		ID	Open (alphanumeric)
		General ID	Open (numeric)
II	Bibliography	Year of publication	Open (numeric)	2010–2023
		List of authors	Open (alphanumeric)
		Publisher 1	Open (alphanumeric)
		DOI 2	Open (alphanumeric)
		Title	Open (alphanumeric)
III	Bibliographic Review	No. of authors	Open (numeric)
		No. of SCOPUS citations	Open (numeric)
		No. of SCOPUS citations (normalized) 3	Open (numeric)
		Source Type	Multiple choice	Journal, Conference paper, Book chapter
		SCOPUS subject area	Multiple choice	SCOPUS nomenclature, NA 5 (for Conference papers, Book chapters)
		SCOPUS sub-subject area	Multiple choice	SCOPUS nomenclature
		Open Access	Multiple choice	Yes, No
		Journal Cite Score 2022	Open (numeric)
IV	Application	Measurable/non-measurable 4	Multiple choice	Quantitative, Qualitative
		Domain	Multiple choice	Socioeconomic analysis, Irrigation method, Water management, Feasibility study, Climate change, Environmental Impact Assessment, Other (specify, e.g., methodology assessment, etc.), combinations
		Methodology	Multiple choice	Managed Aquifer Recharge, Wastewater reuse, Desalination, Rainwater harvesting, Other (specify, e.g., expert knowledge, groundwater extraction, etc.), combinations
		Target	Multiple choice	Agricultural use (crop irrigation, etc.), Urban use (potable use, non-potable use, runoff regulation, etc.), Other (specify, e.g., industrial, environmental, climate change), combinations
		Application period	Multiple choice	Past, Present, Future, combinations
V	Field work	Field activity	Multiple choice	Yes, No
		Type of activity	Multiple choice	Measurements/Observations/Sampling, Modeling, Interviews, Review, Other (specify), combinations, NA
VI	Study area	Continent	Multiple choice	Africa, Asia, Europe, Unspecified
		Country	Open (alphanumeric)	Country Name, Unspecified
		Name of the study area	Open (alphanumeric)
		Scale	Multiple choice	Experimental Site (WW treatment plant, greenhouse, building, etc.), Farmland (plot, field, orchard, olive grove, etc.), Landscape (hillslope, coast, plain, park, golf course, lake, aquifer, etc.), Basin, District, Country, Region, Other (specify), combinations, NA

¹ Journal, Book, Conference title. ² Digital Object Identifier. ³ Estimated as the division of the ‘Total number of citations’ by the ‘Number of years from the year the study was published’. ⁴ Non-measurable refers to an assessment of temporal trends, spatial patterns, and/or driving factors, while measurable delivers numeric results. ⁵ Not applicable.

was extracted from an Excel worksheet to facilitate further analysis. The workflow is depicted in Figure 2.

2.4. Literature Analysis Framework

The review was structured around four key analytical dimensions to ensure a comprehensive understanding of regional patterns and practices. First, the geographical distribution and spatial scale of NCWR applications were examined to identify where and at what levels (local, regional, national) these interventions have been implemented. Second, the temporal distribution and methodological approaches of the studies were analyzed to capture trends over time and assess the scientific rigor and diversity of techniques employed. Third, attention was given to the type of surveys, distinguishing between measurable projects and non-measurable efforts, and their time frame (past, present, future, combinations). Finally, the application objectives were categorized, revealing the dominant drivers behind NCWR use, such as agricultural support, urban water security, or ecosystem restoration. This multi-step approach allowed for a nuanced synthesis of the literature, highlighting both commonalities and gaps across Mediterranean contexts.

3. Results

3.1. Geographical Distribution and Spatial Scale of the NCWR Applications

The geographical distribution of the NCWR DB registries is displayed in Figure 3. The 282 individual records are apportioned to 18 Mediterranean countries and 3 continents. Application density is notably higher at the northern (EU, n = 195, 69.1%) rim of the Basin compared to the southern (Africa, n = 52, 18.4%) and eastern (Asia, n = 25, 8.9%) ones, while 11 studies could not be classified. Spain (83 entries, 29.4%) is the strongest contributor, followed by Italy (43 entries, 15.2%) and Greece (33 entries, 11.7%). More than 50% of the total NCWR studies are conducted in these three countries. Rather low frequencies (<10 entries) are observed in sixteen countries, with six of them (Monaco, Slovenia, Croatia, Bosnia and Herzegovina, Montenegro, Albania) having null (publication) presence. As to the implementation scale (Table 2), most applications take place at the District level (n = 65, 23%), followed by experimental sites (n = 47, 16.7%) and farmlands (n = 45, 16%) (Figure 4).

In terms of extent, farmland-scale applications predominantly utilize WWR by a striking 91.1% (41/45 entries). They are utterly dedicated to the agricultural sector (91.1%, 41/45 entries), field activity occurs in almost all of them (95.5%, 43/45 entries), and the most common type is M/O/S (77.8%, 35/45 entries). More than half of the landscape-scale applications use MAR (54.8%, 17/31 entries), they support agriculture (61.3%, 19/31 entries), perform M/O/S field activity (67.7%, 21/31 entries), and take place in Europe (64.5%, 20/31 entries). Experimental sites are mostly set up in Europe (74.5%, 35/47 entries), utilize WWR and perform M/O/S in half the cases (51%, 24/47 entries), respectively. At the district level, urban uses prevail (43.8%, 28/64 entries), mostly occurring in Europe (92.2%, 59/64 entries), while field activity is not common (73.4%, 47/64 entries). Country-scale studies have only been performed in Europe, largely discussing WWR (66.7%, 20/30 entries). Finally, only one study was performed on a basin scale, while at the regional scale, the results were rather erratic, and no specific trend could be detected.

3.2. Temporal Distribution and Method of the NCWR Applications

A total of 193 contributions were retrieved, spanning from 2010 to 2023. Their distribution in bi-annual clusters revealed an upward publishing trend, apart from the ‘shorter’ 2022–2023 window (Figure 5). Most articles were published during 2018–2019 (n = 34) and 2019–2020 (n = 34). The observed decline (last cluster) is attributed to the fact that data collection was concluded on 30 April 2023, thereby excluding the remainder of the year from the analysis.

The WWR method was dominant throughout the surveying period (n = 89, 46.1%) and within clusters, followed by RWH (n = 48, 24.9%) and Desalination (n = 25, 13%). MAR (n = 17, 8.8%), combination schemes (n = 8, 4.1%), and other approximations (n = 6, 3.1%) were less implemented. Most studies per interval and in total (n = 131, 67.9%) were performed in Europe, followed by those conducted in Africa (n = 36, 18.7%) and Asia (n = 22, 11.4%).

3.3. Type and Time Frame of Surveys

The studies are categorized as measurable (n = 209, 74.1%) and non-measurable (n = 73, 25.9%), appearing in the DB in a 4:1 ratio. The former deliver solid numerical results, whereas the latter provide a more ‘theoretical’ analysis of benefits and limitations, spatial patterns, temporal trends, and future predictions, natural and socioeconomic drivers, etc. Both approaches appear on all continents, but in a rather erratic manner.

Studies discussing NCWR applications in the present (n = 206, 73%) and in combined temporal frames (n = 50, 17.7%) represent most of the entries in the DB (~91%). Future projections (n = 21, 7.4%) and past analyses (n = 5, 1.8%) are less common.

3.4. Application Objectives

The studies are grouped according to their objective into agricultural (crop irrigation, etc.), urban (potable water, non-potable use, runoff regulation, etc.), other types/uses (industrial, environmental, climate crisis, etc.), and combined approaches (Figure 6a). The NCWR DB shows an evident dominance of agricultural applications (n = 131, 46.5%). Urban uses (70 registries) constitute 24.8% of all entries, followed by the almost equally appearing joint implementations (n = 63, 22.3%). Other aims (n = 18, 6.4%) make a minor contribution.

In a more specific classification, the applications were further clustered into seven scientific domains, namely bibliometric analysis (n = 2, 0.7%), climate crisis (n = 6, 2.1%), environmental impact assessment (EIA) (n = 28, 9.9%), feasibility study (n = 10, 3.6%), irrigation method (n = 35, 12.4%), water management (WM) (n = 120, 42.6%), socioeconomic analysis (n = 9, 3.2%), other type, e.g., methodology assessment, etc. (n = 8, 2.8%), and their combinations (n = 64, 22.7%) (Figure 6b). Nearly half of the NCWR applications deal with WM. The other half is disproportionately appointed to the remaining fields.

As to the analysis procedures employed, Measurements/Observations/Sampling (M/O/S) is the most common field activity with 94 entries (33.3%), followed by modelling applications with 52 entries (18.4%). Other types of NCWR mapping in the Mediterranean Region are less frequent, involving reviews, combined approaches, and interviews, with 36 (12.8%), 10 (3.5%), and 7 (2.4%) registries, respectively. For the remaining 83 studies (29.4%), no relative information was available (Figure 6c).

4. Discussion

The scatter of NCWR practices across the Mediterranean countries, and between the northern and southern rims of the Basin, is the result of contrasting socioeconomic and natural conditions. Socioeconomic differences are shaped by the varying levels of financial development, population density, scientific and technological advancement, and regulatory and institutional capacity. Differences in natural conditions comprise variations in climate, resource availability, terrestrial morphology, and ecosystem challenges. This heterogeneity has led to different approaches in WRM. In general, EU countries (northern Mediterranean) have higher levels of economic development and technological capacity. This allows for significant investments in advanced water treatment technologies (e.g., desalination with reverse osmosis, membrane bioreactors), characterized by costly establishment and expensive and energy-consuming operation. Spain, for example, has become a global leader in desalination, particularly in regions like Alicante and Murcia, due to substantial investments in desalination plants. Treated WW is increasingly used for agricultural and landscape irrigation in Spain and Italy [150]. The availability of EU funds and subsidies supports the development and maintenance of such infrastructure. Although application density between the two rims seems to contradict our general perception of the geography of aridity conditions and the lower per capita water availability [30]—expected to be more intense at the northern African and western Asian shores (see relevant literature on water stress levels and aridity index; drought index values in the Mediterranean)—it is essentially justified by the higher capacities of the EU MS. Conversely, Southern Mediterranean countries are still catching up due to economic and technological constraints. In Morocco, for instance, treated WW is used for irrigation, but the scale remains relatively small. This limits their ability to invest in and maintain sophisticated water treatment and desalination infrastructure. Despite the efforts to increase the use of desalinated water, e.g., in Tunisia and Algeria, financial and technical barriers often hinder large-scale implementation. Hence, they resolve to rather simpler solutions like expert knowledge, which might be less efficient, and/or rely on international aid and loans, which can be inconsistent and politically influenced. This disproportionate distribution also correlates with higher population densities and greater urban water demands in the northern subregion, which incentivize the development and study of NCWR solutions [151,152]. Finally, there is also the perception that mitigation urgency is not the main driver that governs the spatial allocation of NCWR (environmental, in general) applications, but rather the needs in tandem with the scientific commitment of research groups in a topic, and their interest in publishing their results in international literature. This is reported by García-Ruiz et al. [153] in their meta-analysis of global soil erosion rates. Our feedback from this regional review leads us to believe that the same applies in this case as well.

The predominance of district-level initiatives reflects the fact that NCWR strategies are often embedded within regional or sub-national planning frameworks, which are better positioned than either national governments or individual users to integrate land use, infrastructure, and water governance across multiple sectors [154,155]. District-level authorities typically have both the jurisdictional scope and institutional flexibility to implement pilot projects, coordinate stakeholders, and respond to localized water stress, especially in areas where water scarcity intersects with population density and agricultural activity [31,156]. Moreover, focusing implementation at the district level facilitates scalable, transferable interventions that can later inform broader national strategies [157]. It also suggests a recognition of the need for territorially tailored solutions—a middle ground between the small scale of farm-level applications and the generality of country-wide policies. This pattern has important implications: it highlights the critical role of meso-scale governance in upscaling NCWR practices and suggests that future investment and policy support might be most effective when directed at this intermediate spatial scale, where both bottom-up needs and top-down planning objectives can be reconciled [158].

An overall rising trend of NCWR publications is identified, which reflects the escalating concern of the scientific community to increase resilience against the growing demand for agricultural (and potable) water availability. As in the case of geographical distribution, the financial resources allocated for applied and theoretical research and data availability—both valuable Research & Innovation (R&I) tools—diversify the Basin’s northern rim from the southern and eastern ones [159,160]. From the early Framework Programmes (FP) funded by the European Commission (EC) at the beginning of the 1980’s as strategic drivers of basic research, to the latest 2021–2027 Horizon Europe Programme with a budget of circa €95.5 B and its associated Missions [161], the EU has been diachronically supporting R&I in the attempt to advance science and tackle complex large-scale cross-sectoral challenges [162]. Since the beginning of the 21st century significant amounts of money financed ‘eco-based’ subject areas, i.e., climate change (20% of available EU funds, i.e., approx. €20.3 B during 2014–2020 [163], expected to rise to a minimum of 35% during 2021–2027 [164]), water quality, carbon, etc., while 2015 was a milestone of the EU funding policy with the adoption of the UN SDGs [47]. The inter-disciplinary character of such projects requires the participatory engagement of diverse networking channels, leading to publication volume escalation. As to data sharing, the Community Research and Development Information Service (CORDIS) public repository, the legal framework of the EC for the re-use of its own data managed by the Publications Office of the EU (https://data.europa.eu/en, accessed on 25 April 2025), and the Open Data Directive [165] further promote the surge in scientific papers. The opposite holds true for the less developed countries (e.g., even the inability of local researchers to fund the publication of their work in international journals), adding to the bias of this study.

Besides, the EU’s stringent water quality and environmental regulations drive the adoption of advanced water treatment practices. The Water Framework Directive [33] is a key policy that promotes sustainable water use across Europe [33]. Together with other ‘green’ policies, i.e., the European Green Deal (EGD) [166], the (incorporated) Zero Pollution Action Plan [167], etc., form a solid framework of obligatory and optional ecological measures, ensuring safe and sustainable practices. There is also strong institutional support, with robust organizations and agencies responsible for managing and implementing NCWR projects. Legislation barriers still exist, summarized in top-down approaches with limited active involvement of beneficiaries, maladaptation of EU directives to national regulatory frameworks, outdated laws that fail to address the uncertainty of the climate crisis, and unsustainable irrigation water pricing. On the other hand, water management policies in the southern Mediterranean are often less developed and are strictly enforced compared to their northern counterparts. This can lead to inefficiencies and delays in the adoption of NCWR use practices [168].

In this context, the limited adoption of MAR and combined NCWR approaches can be attributed to a range of economic, technological, and governance-related barriers. MAR systems often require complex hydrogeological assessments, long-term monitoring, and site-specific engineering, which increase costs and limit scalability in data-scarce regions [169,170]. Similarly, integrated or hybrid NCWR solutions entail higher investment and coordination across sectors, posing institutional and financial challenges, especially in regions with fragmented water governance [171]. Additionally, public acceptance, regulatory uncertainty, and inadequate technical capacity can further hinder their uptake compared to more straightforward and well-established methods like WWR or rainwater harvesting RWH [172].

Concerning public awareness, citizens and ‘actors’, i.e., farmers, farmer associations, enterprises, policy makers, local governments, etc., of the northern rim are more informed about water scarcity issues and the benefits of NCWR, and they have a higher acceptance rate for agricultural and industrial applications. In farmlands, their use is supported by extended, efficient irrigation systems compatible with NCWR (drip irrigation) and the cultivation of high-value crops, ensuring economic returns that justify such investment. Conversely, southern rim farmers predominantly use less efficient irrigation methods (flood irrigation), while in subsistence cropping, the economic feasibility of using NCWR is always a concern. Lifestyle and consumption habits (dietary, clothing, etc.) that require resource-intensive agricultural practices, the type of land ownership (tenure), and the associated caretaking of resources are important issues that also diversify geographically. Other societal constraints, such as the attachment to traditional practices (dubiousness to embrace novelty or abandonment of cultivation systems of high conservation value, e.g., terracing); skepticism stemming from community perspectives; and the needs, priorities, and reluctance of farmers to participate in collaborative synergies have transboundary characteristics. Public awareness and the effective implementation of innovations related to NCWR are also closely linked to the quality of education and its orientation toward environmental sustainability. Educational systems that embed water literacy, environmental ethics, and problem-solving skills from an early age tend to foster more receptive and informed societies, better equipped to adopt and support NCWR initiatives [173,174]. In the Mediterranean region, however, there are significant disparities in both access to quality education and the integration of environmental themes into curricula. Northern Mediterranean countries (e.g., Italy, France, Spain) often incorporate environmental education through formal and non-formal channels, while many southern and eastern Mediterranean countries face systemic challenges such as underfunded education systems, lower enrollment rates, or less emphasis on sustainability in school programs [31]. These gaps can influence public attitudes toward water reuse, desalination, and rainwater harvesting, potentially slowing the uptake of innovative NCWR solutions where awareness and trust are limited.

Regarding natural conditions, the northern Mediterranean typically experiences (at least prior to the climate crisis) a relatively moderate climate that helps sustain more consistent water supplies, while the higher rainfall rates contribute to more abundant freshwater resources. However, precipitation patterns can still lead to periods of drought, and urbanization and tourism in coastal areas can strain water resources, making NCWR a valuable supplement [175,176]. The acute arid conditions and freshwater scarcity of the south notably increase reliance (even necessitate for survival) on the NCWR [168]. Hence, arid and semi-arid zones (e.g., southern Spain, Israel, parts of North Africa, and the Middle East) tend to prioritize WWR and desalination, where freshwater scarcity is acute and infrastructure exists to support these technologies [177,178]. Mediterranean sub-humid zones (e.g., northern Italy, parts of France, and Greece) show more frequent applications of RWH and MAR, often supplementing conventional sources to meet seasonal demand peaks [93]. Urban and coastal zones, regardless of climatic classification, often adopt desalination or reclaimed wastewater for municipal and industrial uses, driven more by water demand than rainfall patterns [31]. The diverse topography in the north supports varied water management strategies, including the use of dams and reservoirs and natural water bodies (rivers, lakes) in the mountains [134], while the southern geography (extensive desert areas, limited river systems, and long coastlines) calls for a stronger focus on desalination (coastal areas) and WW treatment (inlands). As to ecological pressures, both regions face significant challenges, but the south is more heavily impacted by extreme conditions such as desertification, soil salinization, high evaporation rates, etc., necessitating more urgent and innovative solutions in water management.

Regarding the analysis procedures employed, Measurements/Observations/Sampling is the most common field activity (33.3%). Therefore, a significant portion of the research is based on secondary data (Data collected, processed, and often published by someone other than the current researcher. It is essentially pre-existing data that is repurposed for new research objectives. Some examples include Government reports and statistics (e.g., national water use, population data), published scientific articles and datasets, historical weather or hydrological records, data from international organizations (e.g., FAO, UNEP, World Bank), institutional monitoring data (e.g., from water utilities or environmental agencies)) or modelling (18.4%). While both approaches offer valuable insights across large spatial and temporal scales, they do present certain limitations that can affect the robustness of findings. These include potential issues with data quality, resolution, relevance, and age, as well as the assumptions and uncertainties inherent in modeling approaches. Additionally, the lack of ground-truthing and limited incorporation of local contextual knowledge may reduce confidence in some results. However, many studies overcome these challenges by validating models with independent data, combining multiple data sources, performing sensitivity analyses, and transparently communicating assumptions and uncertainties. The integration of remote sensing and long-term monitoring further enhances reliability. While empirical measurements remain essential, the thoughtful use of secondary data and modeling continues to provide a strong and practical foundation for understanding and managing NCWR in diverse and complex Mediterranean environments.

5. Impacts of NCWR Technologies

The use of NCWRs holds significant potential to address water scarcity, but it also presents environmental and social impacts, and other concerns (technical, financial, regulatory) that must be carefully managed. Identifying and mitigating these risks is essential for ensuring that NCWRs are sustainable, socially acceptable, and eco-friendly.

5.1. Environmental Impacts

5.1.1. Managed Aquifer Recharge (MAR)

Recharging aquifers with treated WW or stormwater can potentially contaminate groundwater supplies if the water is not adequately treated. This can introduce pathogens, nutrients, and chemicals into drinking water sources, posing risks to public health.

5.1.2. Rainwater Harvesting (RWH)

The deficit of irrigation water [179], the deprivation of downstream users of shared water resources [180], the impact on local hydrological cycles (reducing the amount of water that replenishes groundwater aquifers or rivers, potentially leads to downstream impacts on ecosystems that depend on natural water flows), microbial contamination risk (in the case of improper maintenance; posing risks for human consumption or use in irrigation), the irregular supply [181] and the small-scale character that defines their complementary role, are common drawbacks of the RWH technology.

5.1.3. Wastewater Reuse (WWR)

The method’s efficiency is limited by the WW quality (concentration of dissolved salts and trace elements) and the treatment level (certain contaminants like pharmaceuticals, microplastics, and heavy metals may persist). Hence, it is more successful when implemented in salinity-tolerant plants, e.g., turfgrasses, fodder crops, shrubs, specific vegetables (tomato, watermelon), and agroforest species, following a secondary (even tertiary) treatment. Otherwise, its systematic application may lead to food security issues due to low productivity, soil salinization and toxicity, and crop contamination [182,183].

5.1.4. Desalination

Desalination is not a problem-free solution, especially compared to conventional water supply methods. Its main drawbacks are the (i) increased energy demands [184,185,186,187], (ii) use of fossil fuels to cover energy needs and the subsequent greenhouse gas (GHG) emissions [128,188]—merely ~1% of the produced DSW globally is based on renewable energy [189]; this can undermine efforts to reduce carbon footprints, (iii) impacts of brine disposal on marine life (by increasing salinity, reducing oxygen levels) [190,191], (iv) impacts of irrigation applications, i.e., soil structure and productivity due to sodium accumulation [192], lack of crop nutrients [193], compliance with stringent boron and chloride standards [194].

5.2. Non-Environmental Impacts

NCWR technologies can also present non-environmental challenges that obstruct their successful adoption and equitable benefits. For example, concerns are raised about the public acceptance of RWH projects [195]. Besides, there is skepticism among consumers [196,197] and farmers [198] regarding the quality and price profitability of desalinated water. Both attributes depend on the facility’s location (fuel availability on the islands is typically lower, increasing operational costs, i.e., transfer and distribution to distant inland sites become more expensive), the fluctuation of electricity prices, the technological level/type of process used, maintenance requirements, the intake water quality, the volume of DSW. Such costs can exacerbate inequalities, particularly in low-income or rural communities. Wealthier urban areas may benefit disproportionately, while marginalized communities continue to face water shortages. Ensuring affordable access, especially for low-income households and small farmers, is a critical social challenge. The high initial capital investment for infrastructure development and the high operational and maintenance costs (especially in the case of desalination) can limit the ability of governments, particularly in low-income regions, to scale up this technology. Moreover, in some regions, there may also be cultural or religious barriers to the use of treated water, especially in agricultural practices or domestic use.

The successful implementation of NCWR projects often depends on effective governance and stakeholder engagement. A lack of transparency in decision-making or failure to involve affected communities can lead to public distrust and opposition. In some cases, such projects may be developed through public-private partnerships, raising concerns about the privatization of water resources and control over pricing and access. After all, in many Mediterranean countries, the regulatory frameworks governing the use of NCWR (water quality standards for WW reuse) are still underdeveloped or inconsistently enforced. This can create uncertainty and hinder investment in NCWR projects. Additionally, the successful implementation of NCWRs often requires coordination between different sectors (water, agriculture, energy) and between different levels of government. In this case, institutional fragmentation can be a significant barrier to integrated water resource management.

Site-specific characteristics must also be considered. For example, the introduction of large-scale NCWR infrastructure, such as desalination plants, may disrupt traditional livelihoods that depend on natural water sources (e.g., small-scale fishing communities affected by changes in marine ecosystems). Thus, not all NCWR technologies are suitable for every region in the Mediterranean. Desalination may not be practical in areas without easy access to seawater, and WW reuse may face limitations in areas lacking sufficient WW treatment capacity.

6. Methodological Limitations

Literature review (as bibliometrics) is an emerging state-of-the-art tool for the synthesis and comprehensive analysis of large volumes of indexed academic data concerning any research topic. However, it comes with certain limitations that can affect the depth, comprehensiveness, and validity of the review. Typical bottlenecks encountered in our study are the limited databases or sources (our study only relied on SCOPUS, meaning that some items may not have been included; research might have been missed if it was published in less accessible or non-indexed journals), the selection bias [only certain types of studies (e.g., peer-reviewed journal articles, books, and conference proceedings) were included, while others (e.g., theses, or industry reports) were excluded], the language bias (we disproportionately focused on literature published in English, potentially excluding valuable studies written in other languages; this may have led to cultural or regional biases in the conclusions of the review), the lack of research on certain topics (insufficient data on certain populations, geographic regions, or specific variables, e.g., given the limited funds available for research and publishing), the geographical or cultural limitations (literature from certain regions or cultural contexts was not applicable to other settings; for example, research in high-income countries was not relevant to low-income regions due to differences in infrastructure, health systems, or social norms), and the interpretation bias (we may have unintentionally imposed our own biases or perspectives on the categorization and organization of the literature, and the interpretation of findings, leading to skewed conclusions or overemphasis on certain studies while neglecting others).

Moreover, this review acknowledges the existing imbalance in research output between the northern and southern Mediterranean regions, largely reflecting disparities in research infrastructure and funding. As a result, literature is more heavily weighted toward northern countries, which may limit the representativeness of findings across the entire basin. To partially address this, we highlight the need for greater attention to underrepresented areas, such as North Africa and the Eastern Mediterranean. Bridging this gap will require enhanced research capacity, increased funding, and stronger collaboration with institutions in the southern region. Existing frameworks—such as the PRIMA Initiative [199], the Union for the Mediterranean [200], and the SWIM-H2020 Support Mechanism [201]—offer promising platforms to support more inclusive research and knowledge exchange. Future studies should leverage these mechanisms to promote a more balanced and comprehensive understanding of non-conventional water resources in the Mediterranean.

7. The Way Forward

Stakeholders, including policymakers, water managers, researchers, community leaders, can use the study’s findings to enhance water management in the Mediterranean Basin—and particularly in the southern rim countries—by translating insights into practical strategies, informed decision-making, and tailored interventions. The identified technical and non-technical barriers will be overcome through a mix of policy, technology, financial mechanisms, and public engagement. Potential strategies include:

• Policy, institutional, and regulatory frameworks
  • Strengthening legal framework: Establishment of clear regulations for the safe use of NCWR, e.g., develop or refine water quality standards for WW reuse, desalination, rainwater harvesting.
  • Policy harmonization: Identify common principles or frameworks from different areas that could be harmonized. This may lead to more coordinated regional policies that foster collaboration on cross-border WRM.
  • Regional cooperation mechanisms: Investigate opportunities for collaborative networks. This may include joint transboundary NCWR projects between neighboring countries with common challenges (e.g., shared treatment facilities of WW) and/or partnerships across disciplines (e.g., engineers, economists, social scientists, environmentalists). There are several existing mechanisms that facilitate regional cooperation on NCWRs in the Mediterranean. The Union for the Mediterranean (UfM) promotes integrated water governance through its Water Agenda and initiatives like the Mediterranean Water Knowledge Platform [200]. The Middle East Desalination Research Center (MEDRC) fosters cross-border collaboration on desalination and water reuse, including joint projects among countries such as Israel, Jordan, and Palestine [202]. The SWIM and Horizon 2020 Support Mechanism, funded by the EU, has supported pilot projects and capacity-building efforts related to water reuse in several Southern Mediterranean countries [201]. Similarly, the PRIMA Initiative funds transnational research on water scarcity and NCWRs, including projects on managed aquifer recharge and wastewater reuse [199]. These initiatives illustrate that regional cooperation on NCWRs is not only ongoing but also well-documented in both policy frameworks and scientific literature.
  • Incentivize innovation: Offer financial support (subsidies, grants, tax reliefs, market-based instruments) for businesses and farmers that adopt/invest in NCWR technologies.
  • Integration into climate policies: Embed NCWR strategies within broader climate (continuous) adaptation plans to build resilience against droughts, floods, and changing rainfall patterns.
  • Ensure social equity: Design water management systems that ensure marginalized communities have access to affordable and sustainable water resources, preventing disparities in water availability.
  • Decentralized systems: Small-scale desalination plants, rainwater harvesting, and greywater reuse serve rural and urban communities more efficiently.
• Capacity building and public awareness
  • Education and training: Providing training for local water managers, engineers, farmers on NCWR technologies (through technical training programs, regional workshops, collaborative research initiatives) can enhance their adoption.
  • Public awareness campaigns: Understand the social, cultural, psychological dimensions of NCWR adoption, launch campaigns to inform the public about their safety and benefits, reduce resistance due to misconceptions or health concerns and increase public acceptance.
  • Stakeholder engagement: Involve stakeholders (farmers, industries, local governments, communities) in the decision-making processes, ensuring that NCWR solutions are co-developed and tailored to local needs and preferences, improve transparency, build trust and support for NCWR projects.
• Technological innovation and optimization
  • Identify research gaps: Allocate funds to areas that require further investigation, such as the long-term effects of treated wastewater on soil health or the development of more energy-efficient desalination technologies, such as the integration of renewable energy (solar, wind) to reduce their carbon footprint and long-term operational costs.
  • Explore alternative NCWR and innovative nature-based solutions: Conduct research on underexplored water sources such as atmospheric water harvesting (fog or dew collection). Investigate and pilot nature-based solutions, such as constructed wetlands and ecosystem-based (biological) water treatment.
  • Data collection and monitoring: Strengthen data collection systems to (long-term) monitor the effectiveness, social acceptance, and environmental impact of NCWR applications over time. This can improve decision-making and public confidence.
  • Data sharing: Develop and maintain open-access data platforms where water-related data, research findings, and best practices for NCWRs can be shared among Mediterranean countries.
  • Digitization and automation: Leverage advancements in digital technologies, including remote sensing, artificial intelligence, and the Internet of Things (IoT), to improve monitoring, management, and optimization of NCWR systems.
  • Pilot projects and demonstration sites: Initiate regional pilot projects considering successful NCWR case studies, allowing for localized viability testing of technologies under real-world conditions before scaling them up. These projects can serve as benchmarks for broader implementation across the Mediterranean.
  • Region-specific research: Tailor NCWR strategies to local conditions (e.g., desalination in coastal areas, WW reuse in urban agriculture), and scale them according to community needs and available resources.
  • Holistic water-energy-food nexus research: Given the interdependence of water, energy, and food systems in the Mediterranean, researchers should explore how NCWRs can be integrated within this nexus. This could involve optimizing resource use across sectors, for example, by coupling water reuse in agriculture with renewable energy production.
• Economic and financial models
  • Cost-effectiveness studies: Encourage studies that compare the long-term economic benefits of NCWRs with conventional water sources, factoring in growing water scarcity.
  • Public-private partnerships (PPP): Governments can collaborate with private companies to fund, build, and operate NCWR infrastructure. This reduces financial burdens (and risk) on public authorities.
  • International donor support: Tap into international funding programs and climate resilience funds, such as the Green Climate Fund, Horizon Europe, the World Bank, etc., to finance NCWR projects.
  • Circular economy models: Investigate how NCWR can be integrated into circular economy models, where water, waste, and energy are reused or recycled in a continuous loop.

Responsibility for enhancing the uptake and implementation of NCWR must be shared across multiple levels and sectors, with clearly defined roles for different actors. At the core, national and regional policymakers should lead by developing and harmonizing legal, regulatory, and institutional frameworks that support safe and equitable NCWR use. Water authorities and managers are responsible for operationalizing these frameworks, ensuring technical feasibility and integration into existing systems. Research institutions and universities should identify knowledge gaps, innovate context-specific technologies, and support evidence-based policymaking. Community leaders and civil society organizations are vital in promoting public awareness, facilitating stakeholder engagement, and ensuring that local needs and socio-cultural factors are respected. The private sector should play a key role in technological innovation and infrastructure development, ideally through public-private partnerships, while international donors and multilateral organizations can provide financial and technical support, particularly in southern Mediterranean countries. Ultimately, effective NCWR implementation requires a multi-stakeholder governance model, underpinned by cooperation, transparency, and shared accountability.

8. Conclusions

Water sustainability in the Mediterranean Basin is challenged by the rapid demographic growth, urbanization and tourism increase, and the acute aridity, aggravated by the climate crisis. Modern water-related problems stem from climate destabilization (hotter temperatures, evapotranspiration rise, prolonged and more severe droughts), the spatiotemporal variability of supply and the imbalance between supply and demand, the inequitable allocation to competing sectors, quality decline (due to pollution, salinization, etc.), incompatibility between exhaustive agricultural practices and (agro) ecological goals, socioeconomic considerations as to food security and financial growth, maladaptation of conventional urban management systems to contemporary needs. The use of NCWR emerges as a practical, feasible (technically, financially), viable supplement and/or alternative to combat water scarcity and increase climate resilience.

This research helped us improve our understanding of the use of NCWR in the Mediterranean Basin. The study revealed the technologies most frequently implemented, the geographical distribution and spatial scale of the applications, temporal trends, objectives, and relationship with nature and society.

The information delivered paves the way for further investigation. It is the authors’ intention to exploit the channels revealed by performing a follow-up bibliometric analysis, to investigate the relationship between NCWR publications and intellectual structure characteristics, i.e., number of authors, productivity leaderships (author, journal, networking group, institution), publication type (journal, book, chapter, conference proceedings), number of citations, keywords inclusion.

Capitalizing on the findings of the study, stakeholders can improve water management practices, enhance resilience to water scarcity, and address both environmental and social challenges in the Mediterranean Basin. Through informed policy, community engagement, regional cooperation, and technological innovation, NCWRs can play a crucial role in ensuring sustainable water security in the Mediterranean region.