Management of Conventional and Non-Conventional Water Sources: A Systematic Literature Review

Abstract

A global transition in water management is currently underway, marked by the declining reliability of conventional sources and the accelerated adoption of non-conventional alternatives. This shift is driven by escalating pressures from climate change, population growth, and freshwater overexploitation. While the literature on management of water sources (WSs) is extensive, empirical clarity on Hybrid Water Systems Management (HWSM)—the integration of conventional and non-conventional WSs within a single system—remains limited. The present study addresses this gap through a systematic literature review using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) approach, which ensures methodological transparency and applicability. From over 9000+ peer-refereed articles retrieved from three major scientific databases (ScienceDirect, Scopus, and Web of Science Core Collections), published between 1999 and 2024, 44 studies were identified as the most relevant and consequently analyzed. The literature review refines the classification of WSs, distinguishing conventional sources, such as groundwater and surface water, from non-conventional alternatives, such as desalinated water, treated wastewater, gray water, and rainwater harvesting. The analysis also indicates that non-conventional WSs are now more prominent in the literature than conventional ones. Overall, the present study demonstrated that modern water management strategies increasingly emphasize optimization and circular reuse. In contrast, earlier approaches tend to focus more on water conservation and economic efficiency. The literature also indicates a gradual shift from traditional supply-dominant models toward integrated, cost-effective, and sustainability-oriented approaches that combine multiple sources and advanced allocation techniques.

1. Introduction

Water is an essential resource for human survival, economic development, and environmental sustainability [1]. Furthermore, the United Nations’ (UN) Sustainable Development Goal 6 [2] establishes access to safe water as a human right, fundamental to health, dignity, and reducing inequalities worldwide [3]. However, the growing global population, industrial expansion, and climate change are intensifying water scarcity [4,5,6,7]. About 1.9 billion people already live in areas with potentially severe water shortages [8]. This number is expected to rise to approximately 3 billion people by 2050, placing immense pressure on available water resources [9]. As a result, water sources (WSs)—both conventional and non-conventional—have become a focus of interest and have attracted significant attention from researchers [10,11,12,13,14,15,16,17], as well as ordinary Internet users (Figure 1).

Traditionally, conventional WSs, such as surface water (e.g., lake water, river water, reservoirs) and groundwater (e.g., spring water, well water), have been the primary means of meeting domestic, agricultural, and industrial water needs [12,19]. However, these WSs are increasingly under stress due to over-extraction, pollution, and changing precipitation patterns [20,21,22].

In response, non-conventional WSs (e.g., desalinated water, treated wastewater, greywater, rainwater) have emerged as viable alternatives to supplement water supplies [23,24]. Desalination, for example, has become necessary in arid and semi-arid regions where the natural availability of fresh water is limited [25,26]. Similarly, wastewater treatment and reuse contribute to a circular water economy, offering opportunities to reuse water for irrigation, industry, and even potable use [27,28].

Despite these advancements, integrating conventional and non-conventional WSs within a single management system remains a serious challenge. The effectiveness and sustainability of such systems depend on many factors, including economic feasibility, energy consumption, physical/technological constraints, public perception, and regulatory constraints [29,30,31]. Moreover, water resource management is often fragmented, with different institutions separately managing surface water, groundwater, desalination, and wastewater reuse, leading to inefficiencies and conflicts in allocation strategies [32,33]. Thus, a comprehensive understanding of how these diverse sources can be integrated to optimize water security is crucial.

In a recent study, Gárate-Ríos et al. [34] reviewed the water resource management literature from 2016 to 2021 across multiple databases, identifying an urgent need for new management paradigms that integrate economic, social, and environmental pillars. Similarly, Sriyono [35] identified five dominant research topics based on Scopus data available as of 2020: water resources, water quality, governance, sustainability, and climate change. These topics reflect a growing call to expand the scope of water management to include socio-environmental systems.

Expanding the scope, Ciampittiello et al. [36], analyzing the literature from 1990 to 2022, stressed the importance of integrating ecosystem protection and restoration within water governance frameworks. This ecological emphasis is also supported by emerging approaches like nature-based solutions and circular water systems, which aim to align water management with environmental sustainability.

Agricultural water use, which globally accounts for over 70% of freshwater withdrawals [21], has been a prominent concern. Hasan et al. [37] reviewed the literature from 2016 to 2023 and identified trends in sustainable water management, including the adoption of water-efficient technologies (e.g., drip irrigation and mulching), transboundary cooperation, and participatory governance. In addition, Rbaibi & SahibEddine [38] identified that effective resolution of interrelated WS challenges is closely linked to integrated management through the Water–Energy–Food Nexus approach.

While numerous studies examined the literature on WSs, existing literature reviews that examine the management of WSs from different perspectives do not focus on the unique characteristics of combined conventional and non-conventional water systems management. To date, most bibliographic literature reviews on WS management remain subjective in terms of document selection, relying on qualitative synthesis or focusing on a single, narrowly defined aspect of the topic. Thus, a holistic approach based on an interdisciplinary literature review is needed to identify the full range of studies focused on integrating conventional and non-conventional water sources within a single management system, hereafter referred to as Hybrid Water Systems Management (HWSM). However, to the best of our knowledge, no systematic literature review of this type has been published to date.

The present study aims to fill this gap by identifying existing research on HWSM, with a focus on the joint management of conventional and non-conventional water sources within a single integrated system.

To achieve this goal, this study adopts the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) methodology. Unlike traditional approaches such as content analysis [39], co-citation analysis [40], or citation-based clustering [41], which can involve subjective decisions and limited scope, PRISMA provides a structured, fully replicable framework for identifying and selecting relevant studies [42,43]. It utilizes Boolean search queries to retrieve studies from the literature systematically [44] and employs tools like Covidence for screening and data extraction, thereby reducing potential selection bias and enhancing the reliability of the findings [43,45]. Yet, to the best of our knowledge, no studies carried out to date have attempted to use the PRISMA methodology in order to determine the comprehensive list of existing research on the management of conventional and non-conventional water sources within a single management system.

The review identifies the main conventional WSs—groundwater, surface water, and fresh/potable water (used in cases where studies refer to drinking-quality water without specifying whether it originates from groundwater or surface water)—alongside eight non-conventional alternatives, such as desalinated water, treated wastewater, gray water, and rainwater. As the present analysis shows, non-conventional water systems are now more prominent in the literature than conventional ones, indicating a significant shift in water management practices. Modern water strategies increasingly emphasize optimization and reuse, particularly in high-income and water-scarce regions. Overall, trends indicate a shift away from traditional supply-dominant models toward integrated, cost-effective, and sustainability-driven approaches that combine multiple sources and advanced allocation methods.

The remainder of the paper is structured as follows: Section 2 outlines our research approach. Section 3 presents the key findings, highlighting the latest trends and challenges in hybrid water resource management. Section 4 discusses the results of the analysis. Section 5 offers the conclusions, discusses the limitations and suggests recommendations for future research.

2. Materials and Methods

According to the PRISMA protocol guidelines [43], this review consists of a structured sequence of steps: (1) selection of search keywords; (2) selection of search parameters; (3) building and tailoring the search string; (4) conducting the initial search and eligibility assessment, and (5) evaluation of results. A detailed discussion of each step is provided in the subsections that follow.

2.1. Selection of Search Keywords

Following our definition of the search topic as “Management of conventional and non-conventional water sources”, the following search components were a priori defined: the search object (“Water Source *”); alternative terms (“Conventional water *”, “Non-conventional water *”, “Water Supply System *”, “Water Resource System *”); elements (“Surface water *”, “Groundwater *”, “Brackish water *”, “Effluent”, “Greywater”, “Reclaimed wastewater”, “Harvested rainwater”, “Atmospheric Water *”, “Desalinated water *”, “Urban runoff *”). Within this structure, elements represent a subset of the search components that capture specific categories of conventional and non-conventional water. To further refine the search and exclude irrelevant results, we also defined exclusion terms not directly related to the search topic: “Biodiversity”, “Ecology”, “Culture *”, “Hydrodynamic *”, “Design *”, “Energy *”, “Health *”, “Climate”, and “Educat *”, where * represents a wildcat search term. The main search terms used in the present systematic literature review are shown in Figure 2.

2.2. Selection of Search Parameters

A recent study by Gusenbauer & Gauster [46], based on an analysis of 404 systematic literature reviews and meta-analyses, found that only a portion of popular academic databases meet the requirements for systematic literature reviews and are suitable for evidence synthesis using adapted PRISMA and Cochrane Handbook guidelines. Of the 101 academic databases available, the most frequently used and adopted for systematic literature reviews in our research field are Web of Science Core Collection, Scopus, APA PsycINFO, and ScienceDirect [34,35,37,38,47,48]. Therefore, ScienceDirect, Scopus, and Web of Science Core Collections were selected as the main databases for the present study.

According to Zare et al. [49], the roots of integrated water resources management and assessment can be traced back to previous decades, but the field began to expand significantly around the 2000s and gained popularity among researchers, especially since 2009 [47]. As a result, the present study covers the period from 1999 to 2024. However, the effective search period is limited to 2002–2024, as no relevant studies that focus on the management of HWSM were found before 2002.

The literature review includes only original research articles published in English, the dominant language in modern scientific communication [45,50]. However, our study excludes “grey literature” (e.g., government reports, policy statements, professional newsletters, issues papers), focusing on articles published in peer-refereed scientific journals [51]. In addition, we do not limit the search by the organizational affiliation of the authors, the number of co-authors, sources of financial support, or the geographical location of publication, as such criteria were considered irrelevant for the purposes of this study.

2.3. Building and Tailoring the Search String

The initial search employed Boolean operators (“AND”, “OR”, and “NOT”) to structure the queries [52]. Due to individual differences in search functionalities across academic databases [53,54,55], the search syntax was customized for each database individually (see details in Appendix A).

2.4. Conducting the Initial Search and Eligibility Assessment

The initial search was performed on 10 January 2025. Following the initial identification, the titles and abstracts of the pre-identified publications were screened, and duplicate items, along with publications not directly related to the subject of research, were excluded from further consideration:

• Studies on flood risk management unrelated to WS management;
• Studies on water demand forecasting that are not linked to specific WSs;
• Studies of societal inequality in access to water;
• Studies on societal behavior regarding water usage;
• Studies on renewable energy unrelated to water management;
• Studies of pricing in water markets;
• Studies of AI-powered water quality index prediction;
• Studies related to climate change impacts on water resources;
• Studies on specific ICT technologies, including data collection, data Storage, data analysis, data protection, and cybersecurity in water systems.

2.5. Evaluation of Results

The application of exclusion criteria resulted in 165 publications being selected for detailed full-text analysis. This stage allowed us to filter out publications that did not report the required elements, resulting in 44 articles for further categorization and analysis. Following this, essential information was extracted from the pre-identified publications, including the publication year, geographical context, and research domain.

3. Results

3.1. PRISMA Flow Diagram

Figure 3 presents the PRISMA flow diagram, detailing the identification, screening, and inclusion of records at each stage of the analysis. The initial search yielded 9294 publications, which were subsequently narrowed down to 44 publications selected for the current review. For the next step, Figure 4 and Figure 5 visualize the keywords’ co-occurrence as determined by the VOSviewer tool [56], where keywords are represented as nodes grouped into clusters. Larger nodes in Figure 4 and Figure 5 denote terms that occur more frequently in the reviewed publications.

As Figure 4 shows, four clusters were identified: (1) a red cluster focused on groundwater and water conservation, (2) a green cluster on water management, optimization, and wastewater reuse, (3) a yellow cluster on irrigation, economics and agriculture, and (4) a blue cluster focusing on uncertainty, quality, and wastewater. “Desalination” is the central term, strongly linked to groundwater, agriculture, economics, and treated wastewater, indicating its integrative role in the management of non-conventional WSs.

Figure 5 illustrates the temporal co-occurrence of keywords, with colors indicating the median year of publication (from 2012, marked in dark blue, to 2024, marked in yellow). “Desalination” remains the central node, highlighting its core role in research concerning both conventional and non-conventional WSs. The keywords most closely associated with desalination include groundwater, management, economics, agriculture, and reuse, reflecting its intersection with resource allocation, policy, and sustainable development efforts. Meanwhile, keywords such as rainwater harvesting, optimization, and wastewater reuse (marked in yellow) indicate the current research focus, while keywords such as groundwater, economics, and water conservation (marked in darker colors) are fundamental topics that have been consistently studied over time. In other words, the results show that current WSs management strategies increasingly emphasize optimization and circular reuse rather than water conservation and economics.

3.2. Database Split

Among the 44 publications selected for full-text analysis, 25 (56.8%) come from Web of Science Core Collection, followed by 11 (25%) from ScienceDirect and 8 (18.2%) from Scopus (Figure 6). The observed differences in results can be explained by the different thematic focuses of the databases: Scopus database prioritizes disciplines such as humanities, arts, social sciences, and medicine [58], while the Web of Science Core Collection shows a stronger focus on the natural sciences and engineering [59].

3.3. Temporal Trends

Appendix B provides a detailed summary of relevant studies on HWSM. The results show a shift away from traditional supply-dominated models towards integrated, cost-effective, and sustainability-oriented approaches that combine multiple sources and advanced allocation techniques. Thus, optimization techniques ranging from multi-objective programming and heuristic algorithms to dynamic hydroeconomic models are increasingly being used to efficiently allocate WSs, minimize costs, and address uncertainty. Environmental and economic constraints such as water salinity, net present value, and energy costs are also frequently integrated into water allocation models to guide sustainable planning. In addition, reuse strategies involving treated wastewater and greywater are being promoted to reduce fresh/potable water withdrawals, especially for non-potable agricultural and industrial needs.

The temporal trend in the annual number of publications is shown in Figure 7. The results show that the first relevant publication on HWSM appeared in 2002, with low activity until 2012. From 2013 to 2021, interest steadily increased (2–4 articles published annually), with a peak of four papers lasting for several years. Although there was a slight decline after 2022, the number of publications remained relatively high throughout 2023 and 2024. This trend reflects a growing interest in managing WSs in response to climate change and the challenges of urbanization.

3.4. Research Fields and Geographic Coverage

The distribution of publications by the research field is shown in Figure 8. The results show that publications on HWSM cover seven main areas: agriculture; biodiversity conservation; business economics; engineering; environmental sciences ecology; science technology; and water resources. However, the number of publications in the field of “water resources” appears to be the most frequent (20 out of 44 articles analyzed), while the topics of “agriculture” and “biodiversity conservation” are represented by only one publication each (see Appendix B for details).

The geographic distribution of publications is shown in Figure 9. Geographically, most papers on HWSM originated in Israel (12), the USA (10), China (4), Saudi Arabia (4), and Brazil/Greece/Germany (3 each). The predominance of publications from these countries may be explained by national policies promoting water security research, significant water scarcity problems, and significant investments in innovative water technologies.

3.5. Water Sources Categorization

Figure 10 categorizes the WSs into two main categories: conventional and non-conventional. Within these categories, groundwater and desalinated water are the most frequently used sources (22% and 18.44%, respectively), while dredging water and distilled water are considerably less frequent (0.71% each). Furthermore, the fact that groundwater and desalinated water are represented close to each other (22% vs. 18.44%) indicates a comparable level of focus in the HWSM literature.

4. Discussion

The main objective of the study was to identify the full range of studies focused on integrating conventional and non-conventional WSs within a single management system. An additional objective was to summarize the current state of knowledge on the classification of conventional and non-conventional WSs. The review helped to identify main conventional WSs (groundwater, surface water, and fresh/potable water—used in cases where studies referred to drinking-quality water without specifying whether it originated from groundwater or surface water) and eight non-conventional alternatives (desalinated water, treated wastewater, greywater, rainwater, stormwater, brackish water, dredging water, and distilled water), commonly used in empirical studies on the management of WSs. The study also enabled us to rank the identified WSs by their frequency of use in the HWSM literature, reflecting the current state of knowledge on both conventional and non-conventional WSs.

Overall, the literature review showed that modern water management strategies increasingly emphasize optimization and circular reuse, rather than water conservation and economics. Moreover, the results indicate a shift away from traditional supply-dominant models towards integrated, cost-effective, and sustainability-oriented approaches that combine multiple WSs and advanced allocation methods, such as multi-objective optimization and dynamic hydroeconomic modeling.

As mentioned earlier, scholars have investigated water management issues from different perspectives, and several review papers have been published to date [34,35,36,37,38,60]. Of these, only one review [38] used the PRISMA methodology to review integrated water management and analyze how “Water–Energy–Food” nexus approaches have been implemented to support sustainable water management.

The results of our analysis are partly consistent with those presented by Gárate-Ríos et al. [34], who identified an urgent need for new management paradigms that integrate economic, social, and environmental components. Similarly, the results presented by Dinar [60] demonstrate that addressing interrelated water resource challenges can be achieved through an integrated water resources management system that integrates the entire set of water types, including surface water, groundwater, reclaimed wastewater, and desalinated water.

Nonetheless, unlike previous literature reviews on water management, which focused on collaboration and interaction among different stakeholders, economic and modeling approaches, planning, water quality, and the implementation of sustainable development elements [34,35,36,37,38,60]. This review aimed to identify the full range of studies focused on integrating conventional and non-conventional water sources within a single management system.

The current study shows a relatively balanced distribution between conventional and non-conventional WSs, with a slight tendency toward non-conventional sources in the recent literature.

The results highlighted by this literature review show that atmospheric water harvesting remains largely overlooked despite its long-term potential and importance. Furthermore, other important WSs, such as dredging and distilled water, appear in ~1% of the studies included in this literature review.

Although 57% of the studies focused on WS management at the country level and 43% on city-level management, this distribution suggests that the literature covers different spatial resolutions. Given that many water challenges and innovations arise in urban areas, the city-scale perspective remains an essential dimension for further research.

Another noteworthy result of this study is that Israel is frequently highlighted in the reviewed literature as demonstrating a particularly diverse and potentially sustainable water supply system, integrating the largest number of both conventional and non-conventional WSs—eight out of eleven—under a single management system (

Table 1. Diversity of water sources integrated into management systems (based on reviewed studies).

№	Water Type	Water Source	Country
1	Conventional	Groundwater	Brazil, China, Crete, East Africa, Egypt, Greece, Iran, Israel, Italy, Jordan, Kuwait, Malta, Saudi Arabia, UAE, USA
2		Surface Water	Brazil, China, Crete, Greece, Iran, Israel, Jordan, Malaysia, USA
3		Fresh/Potable Water	Brazil, China, Colombia, Greece, Israel, Mexico, Northern Europe, Republic of South Africa, UAE, USA
4	Non-Conventional	Desalinated Seawater	Brazil, Crete, Egypt, Greece, Israel, Italy, Jordan, Kuwait, Malta, Saudi Arabia, UAE, USA
5		Brackish water	Crete, Israel, UAE
6		Reclaimed/Treated Wastewater	Brazil, China, Crete, Gaza Strip, Iran, Israel, Malaysia, Mexico, northern Europe, Saudi Arabia, UAE, USA
7		Rainwater	Brazil, China, Colombia, East Africa, Greece, Israel, Mexico, Republic of South Africa
8		Greywater	Brazil, Colombia, Israel, Mexico, Republic of South Africa
9		Stormwater	East Africa, Northern Europe, Republic of South Africa, USA
10		Dredging Water	China
11		Distilled Water	Kuwait

Note: The table summarizes how WSs and management systems are depicted in the reviewed studies (1999–2024), which may differ from real-world configurations; the table provides details on the geographical distribution of studies using each WS, facilitating the identification of regional trends and preferences.

). As reflected in our results (Figure 9 and Table 1), Israel’s experience is often cited as a global pioneer, combining desalination, wastewater reuse, and conventional WSs into one of the most advanced hybrid frameworks worldwide.

In addition to Israel, Brazil also stands out as a highly diverse country, combining conventional WSs with numerous non-conventional alternatives such as treated wastewater, greywater, and rainwater. Kuwait is a contrasting example, as its extremely limited natural resources mean it relies heavily on energy-intensive technologies such as desalination and distillation.

Surprisingly, while Australia represents a leading case in non-conventional water adoption, particularly during the Millennium Drought [61], it was not highlighted in our PRISMA screening process. This is because many Australian studies focused on a single non-conventional source rather than the management of hybrid water systems that include both conventional and non-conventional sources. This explains their limited representation in the final sample.

Regional patterns are also evident: while Latin America and sub-Saharan Africa place particular emphasis on rainwater harvesting, non-traditional sources such as greywater and treated wastewater predominate in the Middle East. This distribution highlights the adaptability of water management strategies to local conditions, highlighting the importance of household water management (HWSM) as a framework for integrating heterogeneous WSs.

Climate pressures and water scarcity are among the primary reasons for integrating non-conventional sources within HWSM. Similarly, cost considerations—including the energy requirements of desalination and wastewater treatment—are recurring themes in the reviewed literature. Our review complements this existing work by focusing on how these factors interact within the broader hybrid system perspective, highlighting integration strategies rather than analyzing each factor in isolation.

This review also shows that the research gaps in HWSM arise from three main causes: (1) disciplinary fragmentation, where engineering, economics, and environmental studies are developing separately; (2) governance and institutional barriers that limit cross-sector integration; and (3) the relatively recent adoption of non-conventional sources, which necessitate the development of integrated management frameworks. Addressing these challenges requires integrated frameworks that combine hybrid WSs, stronger governance frameworks to improve coordination, and interdisciplinary collaboration to better align technical, economic, and environmental perspectives.

In particular, the study refined eleven operational categories for classifying WSs, grouped into two aggregated groups—conventional (groundwater, surface water, and fresh/potable water—used in cases where studies referred to drinking-quality water without specifying whether it originated from groundwater or surface water) and non-conventional (desalinated water, treated wastewater, gray water, rainwater, stormwater, brackish water, dredging water, and distilled water). This outcome represents a more detailed categorization than that presented by Dinar [60], who identified a set of water types that included surface water, groundwater, reclaimed wastewater, and desalinated water.

The present analysis also helped to rank the WSs by their frequency of appearance in the reviewed literature, showing that groundwater and desalinated water are the most frequently used sources (22% and 18.44%, respectively), while dredging water and distilled water are considerably less frequent (0.71% each). In contrast to the pattern presented by Saleh et al. [62], where groundwater and treated wastewater are the most and least frequently used sources, with 51% and 9%, respectively.

The methodological approach can explain the differences in findings. Previous studies have often used literature review approaches without determining formal criteria for selecting relevant studies, which increased the risk of selection bias. In contrast, our study applied the PRISMA methodology, using the Covidence tool for screening and data extraction procedures [45]. Thus, the PRISMA method reduces potential selection bias and enhances the reliability of the findings [43] compared to other methods such as content analysis [39] or citation clustering [41], which may overlook key bibliographic information due to the absence of study-section protocols.

5. Conclusions

This systematic review, conducted in accordance with the PRISMA methodology, identified and analyzed existing research on HWSM. The review clarified the classification of WSs, distinguishing the main conventional types—groundwater and surface water—from eight non-conventional alternatives, including desalinated water, treated wastewater, gray water, and rainwater. The analysis revealed that non-conventional WSs are now more frequently discussed in the literature than conventional ones, indicating a significant shift in water management practices. Modern water strategies increasingly emphasize optimization and reuse, particularly in high-income, water-scarce regions. Overall, the findings reveal a shift away from traditional supply-dominant models toward integrated, cost-effective, and sustainability-driven approaches that combine multiple sources and advanced allocation techniques.

Several limitations of the present study should be noted. First, the systematic review covers the period from 1999 to 2024. Second, the literature review only includes original articles published in English. However, our study excludes “grey literature” (e.g., government reports, policy statements, professional newsletters, issues papers), focusing on articles published in peer–refereed scientific journals that appear in ScienceDirect, Scopus, and Web of Science Core Collections databases. Finally, only one specific research area was analyzed—management of conventional and non-conventional WSs. It should also be noted that certain global leaders in non-conventional water adoption, such as Australia, are underrepresented in the final sample, as many of their contributions emphasize single-source strategies rather than integrated hybrid systems. Future research should prioritize the evaluation of current knowledge in managing conventional and non-conventional WSs, with a focus on the sustainability and flexibility of WS management.