Assessing Urban Water Footprint: An Integrated Analytical Framework for Urban Systems

Abstract

Water scarcity in urban areas, pollution, and the growing interdependence of resources have led to the emergence of the urban water footprint (UWF) as a significant indicator of urban sustainability. However, research on the UWF has attracted considerable interest from the scientific community, given the methodological shortcomings that currently exist. This paper focuses on available studies on the UWF through a systematic literature review (SLR) using the Scopus and ScienceDirect databases. Following the PRISMA 2020 statement and the quality assessment framework developed by Kitchenham and Charters, a total of 61 studies were identified. The results reveal an increase in the number of studies on the UWF, particularly since 2016, focusing on specific cities where volumetric methods were used to calculate the blue or total water footprint. Other findings highlight changes in application objectives, particularly the shift from descriptive studies to prescriptive studies aimed at policy formulation, water efficiency, water governance, and the assessment of sustainability in urban systems from a water perspective. In summary, this research highlights significant gaps in multiscale and comparative studies, inconsistencies in system boundaries, and a lack of a socio-ecological perspective in the assessment of the UWF.

1. Introduction

Cities represent critical hubs where freshwater demand, pollution, and trade connections converge; they are becoming increasingly important when assessing their total water footprint (Total WF). Urbanization is leading to a dramatic increase in water consumption for domestic, industrial, and public utility uses, as well as for infrastructure and even for the consumption of goods and products manufactured elsewhere. The concept of UWF can also be used to highlight direct water use within urban boundaries, as well as virtual water and indirect water use in consumption and production patterns [1,2].

The indirect and virtual water content of food, energy, goods, and services can be of a similar magnitude to that of water supplied through the urban piped network, especially in countries with high consumption levels [3,4,5]. Furthermore, the Grey Water Footprint (Grey WF) can provide valuable information for assessing pollution pressures and sustainability constraints on receiving water bodies, whose capacity to assimilate pollutants and protect water quality is limited [6,7,8]. Water footprint (WF) pressure is, therefore, more than a local supply issue; it is a complex systemic problem requiring a holistic assessment that encompasses aspects of consumption, economy, spatial organization, technology, governance, and the use of external resources.

Watersheds containing UWFs have been assessed using various methodologies, such as water footprint measurement, multiregional input–output models, life-cycle assessment, and hybrid methods [9]. These diverse approaches have different strengths and limitations related to how the system is described, how the study area is characterized, which aspects of WF are emphasized, and the reasons for their implementation. While some studies have focused on comparing the conditions of the urban and rural components of watersheds [10,11], they have also assessed the impacts of trade-offs on water consumption for supplying specific regions or uses [12,13]; only a limited number have specifically addressed comparisons between WF, the carbon footprint, and the ecological footprint [14,15,16].

Against this background, the present study addresses the following research questions:

RQ1. How has UWF research evolved in conceptual, thematic, and empirical terms?

RQ2. Which methodological approaches have predominated in UWF studies, and how are their application patterns structured?

RQ3. How has the UWF been addressed according to city type, spatial scale, and geographical context?

RQ4. How have the application objectives of UWF evolved, and which urban planning, governance, and sustainability dimensions have been prioritised?

RQ5. What are the main conceptual, methodological, and spatial gaps in UWF research, and which future research pathways can strengthen urban water footprint assessment?

Within this framework, RQ1 examines the evolution of UWF, identifying development phases, analytical shifts, and field maturation processes. Building on this foundation, RQ2 evaluates the methodological approaches employed, assessing their diversity, recurrence, and capacity to represent the complexity of urban systems. Complementarily, RQ3 addresses the spatial dimension of existing knowledge by analyzing how the UWF has been applied across city types, analytical scales, and geographical contexts, enabling the detection of dominant patterns and territorial gaps. From an explicit temporal perspective, RQ4 investigates the evolution of application purposes across successive time windows, revealing transitions from descriptive assessments toward management, policy, and sustainability-oriented applications. Finally, RQ5 integrates the preceding findings to identify structural gaps in conceptual, methodological, and spatial terms, and to outline a future research agenda aimed at strengthening water-sustainable urban systems.

To contextualize the findings of this study, a preliminary bibliometric analysis was conducted to assess the state of the art in this field. A Scopus database search was performed to shortlist reviews and systematic reviews on UWF-related topics. Using VOSviewer software version 1.6.18, the 100 review papers identified by searching Scopus database that contained the search terms of “urban water footprint”, “water footprint of urban”, “urban water footprint assessment”, “water footprint in urban”, “urban water footprint methodology”, “water footprint of urban agriculture”, “urban water footprint of buildings”, “water footprint of households in urban”, “water footprint in urban areas”, “water footprint of urban drainage systems”, “urban water footprint of food industry”, “water footprint of urban municipalities”, “water footprint of urban wastewater treatment plants”, “water footprint of water treatment plants in urban” were mapped using the keyword co-occurrence analysis. Applying the threshold condition of 5 occurrences of 5, 48 keywords were derived from a total of 1021 keywords related to the selected papers (see Figure 1).

While “water footprint” and “review” are frequently used keywords in current review papers, major themes common to the current literature include water footprint, sustainability, agriculture, and water resources. Also, although the keyword “urban water footprint” is only weakly connected to 51 and 78 citations, respectively, it appears that an in-depth investigation of the UWF has not yet been carried out. In other words, urban water-related aspects have not yet been investigated as a main theme in the existing literature. Furthermore, to the best of the authors’ knowledge, a systematic literature analysis (SLR) conducted in accordance with PRISMA guidelines, together with a structured methodological quality assessment of the articles considered for review, has not yet been reported in the literature.

The WF of urban areas has not yet been fully explored in the scientific literature; thus, this study is the first to bridge this knowledge gap. In the current study, an SLR on UWFA is conducted. A structured revision approach following the PRISMA protocol and the methodology framework provided by Kitchenham and Charters (2007) [17] is adopted. This approach secures maximum transparency, reproducibility, and methodological evaluation, leading to the required methodological and conceptual advancements in urban water resources sustainability.

The paper is divided into seven (7) sections. Section 2 is devoted to the background of UWF research. Section 3 is the methodology used in the study. Section 4 gives the results of the study. Section 5 discusses the findings. Section 6 is on the future research agenda. Section 7 is on the study’s conclusions and recommendations.

2. Background

2.1. Water Footprint

The WF concept originated from the so-called virtual water concept, a methodology that aims to quantify the amount of water transferred indirectly through international trade in goods and services [18,19]. It has been proven that the ultimate end use of a product always results in water pressure at a location other than where the corresponding water resources are extracted. This enables a water perspective that goes beyond local water use at the point of end use, far beyond the boundaries of a country, watershed, or even a continent [20,21]. It has also been shown that virtual water flows affect water security and form strong structural relationships among water scarcity hotspots [22].

The principle of WF is a quantitative indicator of the amount of water that is used directly or indirectly by people, products or services [1,20]. A work developed in [23] further elaborated on this principle and explained how WF bridges consumption activities with the hydrological system that supports them. Moreover, it adds spatial and scalar dimensions to the water balance, which are not addressed in the conventional water balance framework [23,24]. The WF indicator is nowadays extensively used to evaluate water sustainability at different scales [25].

The WF is built from three types of water use that reflect different pressures on freshwater resources. The blue water footprint (Blue WF) is the volume of water extracted from freshwater resources (surface and groundwater) that is not returned, or is returned after use, under the same hydrological, climatic, geographical, technological, managerial, and operational conditions [1]. The green water footprint (Green WF) of agricultural products is the amount of rainfall required to meet the transpiration demand of the harvested area’s crop under prevailing climate, soil, and land conditions [26,27]. The Grey WF represents the amount of water required to meet the environmental flip side of the quantity of water removed, or the excess, for the receiving water body to comply with the established water quality standards [28,29].

In this review, Total WF refers to the aggregated volumetric water footprint obtained by combining the green, blue, and grey components when these are reported jointly or when studies provide a single overall water footprint value. This category is used to distinguish studies that report an integrated WF indicator from those that analyzed individual components separately. However, Total WF should be interpreted as an aggregate accounting measure rather than as a direct indicator of environmental impact, since its meaning depends on the relative contribution of each component and on the hydrological context in which water use occurs.

The WF framework integrates the assessment of water quantity and quality. While the majority of indicators relate only to the physical dimension (quantity), the WF also includes the Grey WF, which reflects the extent of water degradation in human-use catchments [30,31]. The WF approach has been widely applied to assess water scarcity and sustainability by evaluating the pressures on water resources arising from water use and contamination processes [32,33].

Methodologically, the water footprint assessment (WFA) can be conducted using bottom-up and top-down approaches. The bottom-up approach provides highly detailed information at the product, process, or company level. It is applied to various WF methods, such as the WFA, LCA, and the ISO 14046 standard [1,34]. ISO 14046 provides the principles for conducting a WF study as a standalone approach or in conjunction with a life cycle assessment. In turn, the ISO TS 14072 standard applies the life-cycle approach at the organisational level [35,36].

The standards for consequential LCA are based on the ISO 14040 [37] and ISO 14044 [38] methodologies and therefore ensure methodological consistency and enable full analytical traceability in large environmental assessments. The operational guidelines for organisational LCA, developed under the UNEP SETAC initiative, have been validated through a series of pilot applications [39,40]. Moreover, ongoing developments will enable us to integrate volumetric and impact-based perspectives into WFA [29,41].

Top-down approaches are alternative or complementary to the bottom-up approach. In contrast to the latter, top-down approaches utilise large-scale macroeconomic models to derive the virtual water content of trade flows at the national or even global level, employing MRIO models [42,43]. Recent studies have confirmed the applicability and efficacy of MRIO frameworks in describing sectoral linkages and unveiling the environmental effects of international trade, making them applicable to a multiscale WF analysis as well [4,5,11].

Originally a qualitative, static approach, this methodology has recently been complemented by dynamic system dynamics (SD) methods to investigate the dynamic behaviour of water systems and reveal their inherent feedback structures [3,16]. By integrating SD with the WF analysis, even the most complex systems characterised by numerous interconnected processes across different spatial scales can be more deeply understood [44,45].

From an evolutionary standpoint, the WF literature exhibits a clear progression from conceptual development toward increasingly contextualised applications. Early phases focused on concept definition and global allocation issues, followed by methodological consolidation driven by standardisation efforts from the WF network and ISO frameworks [1,23]. Since 2018, temporal analyses indicate a substantive shift toward addressing water security, efficiency, and resilience, particularly within urban systems [46,47]. This transition has positioned UWF research as an emerging and strategically relevant domain within the broader field [25,47,48].

2.2. Urban Water Footprint

The UWF is a specific application of the general WF concept. It is applied to describe, in detail, the urban metabolism of water consumption, transformation, and re-distribution in cities as high-density, complex systems. As discussed in the context of Urban Metabolism, water can account for up to 80-90% of all physical inputs considered direct inputs to cities [49,50,51]. However, when considering high-consumption goods often imported from outside the urban administrative boundary, a large number of additional indirect water inputs are included in these products [28,52].

In the context of this review, urban system boundaries refer to the spatial and functional limits used by each study to define the urban unit under analysis. These boundaries may correspond to an administrative city, municipality, metropolitan area, neighbourhood, city-region, or another explicitly defined urban system. They may also include functional relationships beyond the urban administrative limit when studies account for indirect water use, virtual water flows, or supply-chain dependencies associated with urban consumption. This definition was used to interpret differences in spatial scale and to classify studies consistently during the review process.

The UWF is the sum of the direct water uses in urban areas, such as urban water supply, domestic, industrial and sanitary uses. It is directly related to the virtual water content embedded in the urban water supply networks. This so-called indirect or virtual water is an important component of the UWF and is essential for water and food security, especially in water-scarce cities [53,54]. For high-density urban land uses, the blue and grey water components are generally the largest. At the same time, the Green WF are usually neglected or are of little importance, as they are not always available and are not important in situations where water is scarce in urban areas [55,56].

The WF of products, resources and services is calculated in one specific way. This does not apply to cities and towns. In urban environments, the approach for the UWF calculation is modified to accommodate the unique urban structure and connectivity. Therefore, municipal direct water use is derived from bottom-up approaches. In contrast, the virtual water embedded in urban consumption is derived from top-down approaches, such as through environmentally extended input–output models [4,42]. This methodology was improved over the years by following the ISO 14046 standard, which enables the application of LCA principles to urban sustainability assessment, urban planning, and water-energy-food (WEF) nexus analysis [46,57]. From 2018 to 2024, the evolution of the UWF’s methodological approach ensured its development and consolidation as an operational urban water balance index for assessing the efficiency, degree of externalisation, and therefore water security of urban systems [47].

From a comparative perspective, these methodological approaches provide different levels of analytical resolution and interpretative capacity. Conventional WF accounting offers transparent volumetric estimates of direct and indirect water use, but it is less effective in capturing scarcity-related impacts, supply-chain complexity, and cross-boundary dependencies. MRIO-based approaches are more suitable for identifying virtual water flows and interregional dependencies, although they often operate at aggregated sectoral scales that may obscure intra-urban differences. LCA-based methods, in turn, strengthen impact interpretation by linking water use to environmental consequences, but they require detailed inventories and context-specific characterization factors that are not always available for urban systems [1,34,42]. Hybrid approaches seek to overcome these limitations by combining volumetric accounting, supply-chain analysis, and impact-oriented assessment; however, their application in UWF research remains limited and methodologically heterogeneous. This methodological diversity reinforces the need for a systematic synthesis capable of comparing how UWF has been conceptualized, operationalized, and applied across different urban contexts.

3. Materials and Methods

This study employed a systematic literature review (SLR) approach to identify, select, evaluate, and synthesize peer-reviewed literature on the assessment of UWF. The review was conducted in accordance with the PRISMA 2020 statement, and the methodological quality of the included studies was assessed using the Kitchenham and Charters framework [17]. The study selection process is shown in detail in Figure 2. A checklist is provided in the Supplementary Material section. Files were deposited in the Open Science Framework (OSF) under the public project identifier mwcfz. The review process comprised the following stages: study design, protocol definition, selection of information sources, search strategy, data integration and duplicate removal, screening and eligibility assessment, quality assessment, and data extraction and synthesis. Figure 2 details the methodological approach of this research.

3.1. Study Design

A SLR was chosen because the UWF research is multidisciplinary and methodologically heterogeneous, encompassing environmental sciences, water resources, urban planning, engineering, sustainability assessment, and policy-oriented applications. This approach made it possible to identify trends in the literature, methodological patterns, spatial orientations, application objectives, and research gaps. The application of PRISMA 2020 ensured transparency in the identification, selection, eligibility, and inclusion phases, while the Kitchenham and Charters framework was used to assess the methodological quality, transparency, and reproducibility of the included studies. Given the diversity of study designs, spatial scales, and assessment methods, the review adopted a structured narrative synthesis supported by descriptive quantitative analysis, rather than a statistical meta-analysis.

3.2. Review Protocol and Information Sources

A pre-defined review protocol was established before commencing any stage of the review process. The review protocol described the sources and search terms used in the literature search, as well as the inclusion and exclusion criteria, in accordance with the PRISMA guidelines. A bibliographic search was conducted in two international scientific databases, namely Scopus and ScienceDirect. The Scopus database was selected as the principal bibliographic source, owing to its extensive coverage of peer-reviewed articles across the fields of environmental sciences, engineering, and urban sustainability. The ScienceDirect database was selected as a complementary source to have access to the top Elsevier journals [58,59].

3.3. Search Strategy

Existing literature relevant to the study scope was identified using an iterative, transparent, and replicable procedure that followed the PRISMA 2020 guidelines. It began with a broad base in water footprint literature and proceeded toward an increasingly focused body of literature on UWF. The two multidisciplinary databases Scopus and ScienceDirect were consulted. Scopus has strong representation in the environmental sciences, urban planning, engineering, and sustainability, while ScienceDirect, with its strong applied science component, includes many journals and proceedings related to urban issues. All search queries in the TITLE-ABS-KEY language were performed in the TITLE-ABS-KEY search fields of the database, so that all relevant information was obtained from strictly descriptive keywords in the title and abstract of each paper.

The procedure began with an exploratory search using the unrestricted string “water footprint”. This initial step retrieved 2966 records from Scopus and 840 from ScienceDirect, thereby delimiting the full conceptual universe of water footprint research. Subsequently, filters were applied, restricting the document type to peer-reviewed articles and the language to English, reducing the datasets to 2097 and 724 records, respectively. This refinement ensured comparability in methodological reporting and minimised interpretative variability arising from non-peer-reviewed outputs.

Urban specificity was then introduced through two complementary Boolean equations. The first targeted explicit city-scale studies using water AND footprint AND (cities OR city), whereas the second captured broader urban system perspectives using water AND footprint AND urban. These queries yielded 49 and 54 records in Scopus and 14 and 22 in ScienceDirect, respectively. The use of parallel equations allowed the retrieval of both administratively bounded and functionally urban analyses, avoiding systematic exclusion of metropolitan or regional urban interpretations. All records obtained from the four resulting datasets were consolidated into a unified database. This integrated dataset constituted the input for duplicate detection and subsequent screening stages, thereby preserving traceability throughout the review process.

3.4. Data Integration and Duplicate Removal

The records obtained from the urban-focused searches in Scopus and ScienceDirect were exported and integrated into a single working bibliographic dataset. The combined search results yielded 139 records. Before screening, duplicate removal was conducted to ensure that each record was assessed only once. Duplicates were identified by comparing DOI, title, and author information; when DOI information was unavailable or incomplete, title and author matching were used for manual verification.

A total of 39 duplicate records were removed, representing 28.1% of the merged dataset. After duplicate removal, 100 unique records remained for title, abstract, and keyword screening, corresponding to 71.9% of the initially identified records. This process avoided double-counting and preserved traceability between the identification and screening stages required by PRISMA 2020.

3.5. Screening and Eligibility Assessment

After removing duplicate records, the 100 unique records were reviewed based on their titles, abstracts, and keywords. The objective of this phase was to determine whether each record was relevant to the UWFA and whether it referred to an urban, city, municipal, metropolitan, neighborhood context, or an explicitly defined urban system.

To improve consistency during the selection process, explicit spatial classification criteria were applied, as described above. Studies were classified as single-city when the analysis focused on a delimited urban unit, and as multi-city when two or more cities were evaluated comparatively or as part of an interconnected urban system. Mixed rural-urban studies were retained only when the urban component was clearly identifiable, analytically separable, or directly relevant to the interpretation of the UWF. Conversely, studies addressing rural, agricultural, regional, or national systems without a distinguishable urban component were excluded. In cases of partial urban coverage or ambiguous spatial boundaries, classification was based on the most detailed explicit urban scale indicated in the study and on whether the WF results could be interpreted from an urban perspective.

Records were also excluded when the WF was mentioned only conceptually, when no clear analytical assessment was provided, or when the scope of the study did not align with the objectives of this review. Studies addressing multiple environmental footprint indicators were retained only when the WF component was clearly identifiable and analytically separable. This screening phase led to the exclusion of 29 records, representing 29.0% of the records examined, while 71 reports were retained for full-text eligibility assessment.

Next, a full-text assessment was conducted to verify the conceptual, methodological, and analytical relevance of each report. Reports were excluded if they did not provide a quantitative or analytically structured assessment of the WF, lacked sufficient methodological details, or did not allow for interpretation from the UWF perspective. Following this phase, 10 reports were excluded, representing 14.1% of the reports evaluated for suitability. Consequently, 61 studies were included in the final review corpus, equivalent to 85.9% of the full-text reports evaluated, 61.0% of the selected records, and 43.9% of the records initially identified.

3.6. Study Selection Process

The study selection process followed the PRISMA 2020 reporting structure and is summarised in Figure 3. The flow diagram documents the complete sequence from identification to inclusion: 139 records were identified, 39 duplicates were removed, 100 records were screened, 29 records were excluded, 71 reports were assessed for eligibility, 10 reports were excluded with reasons, and 61 studies were included in the final systematic synthesis.

Figure 3 presents the PRISMA 2020 flow diagram used to document the identification, duplicate removal, screening, eligibility assessment, and inclusion of studies. The diagram reports the number of records identified, records removed before screening, records screened, reports assessed for eligibility, reports excluded with reasons, and studies included in the final synthesis.

Before screening, 39 duplicate records were removed based on DOI, title, and author matching. This resulted in 100 unique records for title, abstract, and keyword screening. During the screening stage, 29 records were excluded because they did not meet the scope of the review, particularly due to the absence of an explicit urban focus, the lack of a distinct water footprint analysis, or their focus on non-urban systems.

The remaining 71 reports were sought for retrieval, and all were successfully retrieved for full-text assessment. During the eligibility stage, the full texts were assessed according to the predefined inclusion and exclusion criteria. Ten reports were excluded because they did not provide sufficient quantitative or methodological information on urban water footprint assessment (UWFA), or because the water footprint component could not be clearly isolated from broader environmental indicators.

The final corpus comprised 61 studies, which were included in the systematic literature review. Given the methodological heterogeneity of the included studies, the review did not conduct a statistical meta-analysis. Instead, the final corpus was analysed through a structured narrative synthesis supported by descriptive quantitative analysis.

3.7. Quality Assessment

The methodological quality of the included studies was assessed using the Kitchenham and Charters (2007) framework [17]. Seven quality assessment criteria, labelled as QA1 through to QA7. Each criterion was scored on a three-level scale, with scores of 1.0, 0.5, or 0.0 indicating high, some, or limited compliance with the criterion, respectively. The criteria were related to the methodological features required for high-level synthesis in a systematic review. Specifically, the criteria were as follows: QA1 clear and relevant study objectives and scope related to the research questions; QA2 clear definition of the urban system, including any clarification of type of urban unit and boundaries; QA3 transparency of water footprint method (including any information on methods or assumptions); QA4 data quality (including sources and limitations); QA5 methodological reproducibility (i.e., sufficient information to enable replication of the research); QA6 examines whether indicators and variables are appropriate and justified for the stated objectives; and QA7 analysis limitations, uncertainties and methodological constraints. The quantitative results of the quality assessment are provided in

Table 1. Statistical summary of Kitchenham and Charters’ quality assessment results.

Criterion	QA1	QA2	QA3	QA4	QA5	QA6	QA7
Mean Score	1.00	0.91	1.00	0.73	0.55	0.43	0.39
Standard Deviation	0.0000	0.1938	0.0000	0.2512	0.4445	0.4986	0.4926
Minimum	1.0	0.5	1.0	0.5	0.0	0.0	0.0
Maximum	1.0	1.0	1.0	1.0	1.0	1.0	1.0
% Full Compliance	100.00%	81.97%	100.00%	45.90%	44.26%	42.62%	39.34%

, including means, standard deviations, minimum and maximum scores for each criterion, and the proportion of studies scoring 1.0 for each criterion.

The methodological robustness of the selected studies was evaluated using the Kitchenham and Charters quality appraisal framework. Seven criteria (QA1–QA7) were applied at the full-text level to ensure consistent assessment of validity, transparency, and reproducibility. Each criterion was scored on an ordinal scale (1.0 = full compliance; 0.5 = partial compliance; 0.0 = non-compliance). The results indicate a highly consolidated conceptual structure across the literature. Full compliance was observed for QA1 and QA3 (mean = 1.00; SD = 0.00), confirming uniform clarity in research objectives and explicit description of the water footprint procedure.

Some moderate heterogeneity is present in the boundaries of the urban systems and in the data quality documentation. Accuracy of QA2 is high but variable (mean = 0.91; SD = 0.1938) due to uncertainty about the boundaries of the urban system. Similarly, QA4 has a high standard deviation (SD = 0.2512) due to considerable heterogeneity in the documentation of data sources and limitations. The lowest robustness is found in the reproducibility and methodological scrutiny items. It is noticeable that the average scores and their dispersion in QA5, QA6 and QA7 are systematically lower and that the full compliance rate is below 45%. This indicates a persistent, though not exclusive, problem with the following aspects: lack of replication of methodological procedures or calculations; insufficient description of input parameters or variables used in calculations; and inadequate handling of related uncertainties. As shown in Table 1, UWF research has matured theoretically, yet it still lacks standardised reporting protocols required for reproducible comparative synthesis.

3.8. Data Extraction and Synthesis

The method used for synthesising the evidence is described as a structured narrative synthesis with descriptive quantitative analysis. A narrative synthesis was appropriate because of the diverse objectives of the analyses (objectives are given in the source tables), the variety of spatial units used, the different definitions of urban system boundaries applied, and, most importantly, the wide range of methods and techniques employed in each analysis. Once quality was assessed, the required information was extracted and standardised to facilitate subsequent synthesis of the results.

During data extraction, particular attention was given to the definition of system boundaries used in each study. The reviewed articles were examined according to whether they included direct urban water use, upstream virtual water flows, downstream pollution-related pressures, sectoral disaggregation, and cross-boundary exchanges. Because the included studies applied different methodological frameworks, no ex post harmonization of system boundaries was imposed. Instead, boundary assumptions were recorded and compared as part of the synthesis. This procedure made it possible to identify potential sources of inconsistency, including sectoral overlaps, partial inclusion of supply-chain stages, and risks of double counting when direct water use and embedded virtual water flows were combined without clear separation.

This synthesis focuses on methodological characteristics of UWFA. By examining the assessment methods and characteristics of individual studies, such as the type of assessment method, urban unit definition, WF components examined, data sources, and level of methodological transparency, the studies were reviewed, and the results are summarised using frequency distributions, percentages, and summary statistics where appropriate. These provide an overview of the degree of consistency and/or diversity in the methods applied in the selected assessment studies. Due to the heterogeneity of study designs and contexts within the case studies included in the SR, a statistical meta-analysis was not possible. Instead, a combined qualitative-quantitative approach to synthesis was used to enable comparative analyses of the research methodologies employed in each case study whilst retaining the unique features of each context. This methodology allowed for a clear and transparent interpretation of the results and ensured consistency between the assessment of the study design and quality of each case study and the synthesis and interpretation of the results.

Registration statement: This systematic literature review was retrospectively deposited in the Open Science Framework under the title Assessing Urban Water Footprint: An Integrated Analytical Framework for Urban Systems. The OSF record was created on 31 March 2026, and is publicly available under the project identifier mwcfz. The OSF deposit includes the PRISMA 2020 checklist and supplementary methodological materials supporting the transparency, traceability, and reproducibility of the review process.

4. Results

This section presents the empirical findings from the systematic analysis, organised around the analytical dimensions defined by the research questions. (i) Evolution of UWF Research examines the temporal development of the field to identify phases of emergence, consolidation, and analytical maturation, providing evidence for RQ1. (ii) Methodological pathways and analytical configurations characterise the dominant assessment approaches and recurrent analytical structures applied in UWF studies, addressing RQ2. (iii) Spatial and urban focus evaluates how research has been implemented across spatial scales, urban typologies, and geographic contexts, thereby responding to RQ3. (iv) Application objectives: analyse how the purposes of UWF applications have evolved and which urban system dimensions have been prioritised, contributing to RQ4. Collectively, these dimensions establish a coherent evidence base to support the identification of research gaps and the development of future research directions (RQ5).

4.1. Evolution of Urban Water Footprint Research (RQ1)

The temporal evolution of UWF research reveals a clear structural transformation over the last two decades. Based on the systematic review of 61 peer-reviewed studies published between 2006 and 2026, this analysis addresses RQ1 by examining publication dynamics, growth intensity, and phase differentiation within the field.

UWF research activities began in 2006 at a highly dispersed, low annual productivity level. During the 10 years from 2006 to 2015, only 11 papers were published, corresponding to 18.03% of the total number of papers in the dataset. This low and highly dispersed annual productivity level of papers published during the first decade of research confirms that, at that time, UWF applications were only considered as a specific case within the large body of research on ecological footprint and urban metabolism approaches, as well as on the consumption perspective of the urban resource analysis. This confirms that, at that time, UWF was not yet a consolidated field of knowledge.

In Figure 4, a marked change is observed starting in 2016. Between 2016 and 2026, 50 studies were published, which accounts for 81.97% of the total number of studies. The annual output, much higher than in the previous decade, has shown peaks recurring since 2017. Thus, the period from 2016 onwards is characterised by a sustained upward trend, indicating that the UWF research field is well-established and growing. The linear trend analysis performed for the second period (after 2016) shows a positive slope, in contrast to the slight, unstable slope obtained for the first period.

In the context of the process of consolidation of UWF as a new urban water science concept and issue emerging from urban water science and evolving towards becoming a stable, well-established scientific object, by meaning temporal bifurcation, the first stage is characterised by the occasional publication of papers dealing with early trial and error research and methodologies. In contrast, the second stage is characterised by in-depth research findings through the systematic use of urban-scale modelling and the advancement of UWF towards the mainstream of the sustainability and urban water science literature. This high concentration of UWF research papers published after 2016 shows that UWF, as an ad hoc resource management practice, is evolving toward becoming a systematic scientific object of research. For RQ1, it has been demonstrated that UWF research has progressed from an emerging, widely scattered body of work to a fully fledged, expanding research field. These phases are foundational for the remaining research questions.

4.2. Methodological Pathways and Analytical Configurations (RQ2)

This section addresses RQ2 by examining how UWF research has been methodologically structured, analytically operationalised, and thematically articulated across the 61 studies reviewed. The analysis integrates three complementary dimensions: urban focus, methodological framework, and water footprint typology. This integrated perspective allows for the identification of dominant analytical pathways, methodological concentrations, and structural gaps within the field.

The urban focus in the literature has been towards sustainability and planning, which together account for 54.10%. Of the 17 papers that addressed the focus of urban sustainability, 27.87% were directed towards environmental impact assessments, resource and water consumption, etc. Urban planning is the second-highest focus area, with 16 papers (26.23%). Hence, the UWF is mainly used for assessing the environmental performance of buildings, as well as consumption and resource use, and to evaluate spatial planning and design decisions. Socio-economic urban studies accounted for only 19.67% of the papers, suggesting that consumption patterns and social issues such as equity and access are becoming more important but remain secondary. Other foci, such as urban policy and governance, urban metabolism and efficiency, and urban industry and economic structure, were less represented, accounting for 18.03% and less than 3.30%, respectively (

Table 2. Frequency distribution of analytical configurations in UWF studies.

Urban Focus	References	Articles	Share (%)
Urban sustainability	[8,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75]	17	27.87%
Urban planning	[52,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90]	16	26.23%
Urban metabolism & efficiency	[91]	1	1.64%
Urban policy & governance	[4,9,92,93,94,95,96,97,98,99,100]	11	18.03%
Socio-economic urban	[2,6,101,102,103,104,105,106,107,108,109,110]	12	19.67%
Urban consumption & trade	[111,112,113]	3	4.92%
Urban industry & economic	[114]	1	1.64%
WF Type
Blue WF	[52,75,81,84]	4	6.56%
Green WF	[82]	1	1.64%
Grey WF	[8,65,66,71,78]	5	8.20%
Blue WF-Green WF	[60,61,64,83,90,109,110,112,113]	9	14.75%
Blue WF-Grey WF	[6,72,86,88,93,98,99,107,114]	9	14.75%
Blue WF-Green WF-Grey WF	[63,73,74,76,77,79,80,87,89,95,100,103,104,111]	14	22.95%
Total WF	[2,4,9,62,67,68,69,70,85,91,92,94,96,97,101,102,105,106,108]	19	31.15%
Methodology
WF accounting	[2,6,8,9,60,61,64,65,66,69,70,73,75,76,77,78,79,80,82,83,84,86,89,93,94,99,100,101,102,103,104,105,108,109,112,114]	36	57.14%
IO-MRIO-based frameworks	[4,71,85,87,88,91,92,96,97,98,107]	11	17.46%
Decomposition & indices	[62,67,74,81,95,106,110,113]	8	12.70%
Hybrid-LCA-EF-based	[63,68,72,111]	4	6.35%
Network / Spatial approaches	[52,90]	2	3.17%

).

Table 2 reveals that UWF research is structured around a limited number of dominant analytical configurations. Urban sustainability and urban planning represent the two most frequent areas of application, together accounting for 54.10% of the reviewed studies. This concentration indicates that UWF has mainly been used to evaluate environmental performance, resource consumption, spatial planning, and design-related decisions. In contrast, urban metabolism and efficiency, urban consumption and trade, and urban industry and economic structure remain weakly represented. This imbalance suggests that, although UWF is increasingly recognised as an urban sustainability indicator, its use remains less developed for analysing productive structures, metabolic interactions, and economic drivers of water pressure.

Methodologically, the field remains strongly dominated by WF accounting approaches, which were applied in 36 of the 61 studies. This predominance confirms the operational value of accounting methods for quantifying green, blue, grey, and total WF components in urban contexts. However, it also indicates a methodological concentration around descriptive and volumetric assessment. IO/MRIO-based frameworks, decomposition and index approaches, hybrid LCA-EF-based methods, and network or spatial approaches are comparatively less frequent, despite their greater potential to capture virtual water flows, interregional dependencies, drivers of change, and spatial redistribution of water pressure. Therefore, the methodological structure of the field reflects a tension between the comparability offered by conventional WF accounting and the need for more integrated approaches capable of representing the complexity of urban systems.

The distribution of WF typologies further reinforces this pattern. Total WF is the most frequent category, appearing in 19 studies, followed by assessments that integrate blue, green, and grey WF components. This indicates that many studies prioritise aggregate interpretation or multi-component accounting. However, single-component assessments remain limited, and the explicit differentiation among blue, green, and grey water pressures is not always fully developed. This is relevant because aggregate WF values may conceal important differences between water abstraction, rainwater dependence, and pollution-related pressure. Overall, Table 2 shows that UWF research has achieved a certain level of conceptual consolidation, but its analytical development remains uneven across methodological approaches, WF typologies, and urban-system dimensions.

Figure 5 provides an integrated reading of the analytical pathways that structure UWF research by linking urban focus, methodological framework, and WF typology. The diagram shows that the strongest flows converge toward WF accounting, particularly from urban sustainability, urban planning, socio-economic urban studies, and policy-oriented applications. This confirms that the field is still largely organised around volumetric and descriptive assessment, with Total WF and multi-component WF categories acting as the main endpoints of analysis. While this configuration supports comparability across studies, it also reveals a limited diversification of methodological pathways.

The figure also highlights weaker connections between advanced methods and complex urban-system dimensions. IO/MRIO, hybrid LCA-EF-based, decomposition, and network/spatial approaches appear as comparatively narrower pathways, despite their relevance for analysing virtual water flows, supply-chain dependencies, drivers of change, spatial redistribution, and governance-related questions. In particular, the limited presence of network and spatial approaches suggests that UWF research has not yet fully incorporated the multiscalar and relational character of urban water systems. Therefore, Figure 5 reinforces one of the central findings of this review: UWF research has achieved conceptual consolidation, but its methodological architecture remains concentrated around accounting-based approaches and insufficiently connected to systemic, spatial, and policy-oriented analytical frameworks.

4.3. Spatial and Urban Focus (RQ3)

This section addresses RQ3 by examining how UWF research has been structured across geographic and spatial scales. At the global level, the literature exhibits a strong geographic concentration in Asia, which accounts for 61.90% of published studies. Europe and North America follow with substantially lower shares, while Africa, Oceania, and South America remain weakly represented. This uneven distribution suggests a geographically concentrated knowledge base shaped by regional research capacities and urban water stress contexts (see Figure 6).

Beyond geographic location, the spatial conceptualisation of cities reveals more substantial analytical implications. Nearly half of the reviewed studies (44.26%) adopt a single-city scope, reflecting a dominant tendency to frame UWF within administratively bounded urban systems. These studies predominantly rely on conventional water footprint accounting and emphasise direct blue and grey water use. Multi-city and city-region approaches collectively represent 34.42% of the literature. These spatial scopes are more frequently associated with IO, MRIO, and hybrid frameworks, enabling the assessment of indirect and virtual water flows across interconnected urban systems. However, their limited adoption constrains the field’s ability to capture interurban dependencies and teleconnections fully.

Metropolitan, neighbourhood, and national urban scales remain marginal, each accounting for less than 7% of studies. Neighbourhood-scale analyses, in particular, are rare and focus almost exclusively on blue water use, indicating a gap in fine-scale assessments that integrate indirect water dynamics. Overall, the dominance of single-city approaches reveals a structural bias toward localised assessments. This spatial simplification limits the representation of multi-scalar urban water interactions, highlighting a critical gap in the current UWF literature (see

Table 3. Distribution of UWF studies according to spatial scope.

Spatial Scope	References	Articles	Share (%)
Single city	[2,6,8,61,62,63,64,65,66,67,68,74,76,78,79,80,82,83,85,86,96,98,102,108,109,110,114]	27	44.26%
Multiple cities	[4,9,69,70,84,92,94,95,97,101,106,107]	12	19.67%
National urban	[60,93]	2	3.28%
Metropolitan area	[77,91,104,105]	4	6.56%
Neighborhood	[90,103]	2	3.28%
City-region	[52,71,73,81,88,99,100,111,113]	9	14.75%
Global Multi-city	[72,75,87,89,112]	5	8.20%

).

4.4. Application Objectives (RQ4)

Figure 7 shows that the application objectives of UWF research have evolved from descriptive and diagnostic uses toward more operational, strategic, and governance-oriented applications. Unlike Section 4.1, which examined the temporal growth of publications, this subsection focuses on the functional transformation of UWF applications and on the urban system dimensions prioritised across the reviewed studies.

In the earliest phase, UWF was mainly used as an exploratory indicator to compare urban freshwater dependence, assess structural sustainability constraints, and provide preliminary support for policy formulation [74,75]. At this stage, the indicator had limited operational integration, since applications were weakly connected to sectoral disaggregation, planning instruments, or management frameworks.

A second application pattern emerged with the use of UWF for sectoral and municipal management. Studies in this group applied the indicator to assess pollution-driven water stress, compare urban water-cycle alternatives, support local water management, and examine specific domains such as urban resilience, urban agriculture, water-use efficiency, sustainable consumption, trade, and industrial-sector pressure [52,71,72,73,90,99,100,112,113]. This indicates a shift from general diagnosis toward technical support for urban management.

More recent studies reveal a broader systemic use of UWF. The indicator has been applied to analyse consumption patterns, diets, food security, pollution mitigation, footprint reduction, regional stress, benchmarking, water–energy interactions, industrial allocation, and natural capital approaches [4,65,66,68,70,85,86,87,88,89,96,97,104,105,106,107,108,109,110,114]. These applications show that UWF is increasingly used not only to measure water pressure, but also to interpret the drivers and consequences of urban consumption and development.

The latest applications place greater emphasis on efficiency, governance, equity, and sustainability transitions. Recent studies address hotspot identification, hidden dependencies, economic decoupling, productive optimisation under water stress, inequality reduction, Sponge City approaches, carbon–water integration, nature-based solutions, urban renewal, scarcity management, and water security [9,60,61,63,64,77,79,80,91,94,95]. Overall, Figure 7 indicates that UWF has progressively moved from a descriptive accounting indicator toward a decision-support tool for urban planning, water governance, and sustainability-oriented transitions. Nevertheless, applications related to water justice, institutional implementation, and long-term impact assessment remain comparatively underdeveloped.

Between 2017 and 2021, the research agenda consolidated around complex urban systems and socioeconomic dynamics, comprising 49.18% (n = 30). Studies intensified analyses of urban consumption, diets, and food security as drivers of water pressure [104,105,107,108,109,110], alongside pollution mitigation and load-control strategies [65,66]. Simultaneously, research addressed footprint reduction under urban growth and regional stress [4,87,88,96], alongside driver analysis, change decomposition, and urban benchmarking [70,89,97,106,114]. Additional integration of the water–energy nexus, industrial allocation, and natural capital approaches [68,85,86] indicates the expansion of the water footprint as a systemic analytical and strategic instrument for urban planning.

Finally, in 2022-2026, representing 32.79% (n = 20), a marked orientation toward efficiency, governance, and operational sustainability emerges. Applications focused on identifying hotspots and hidden dependencies in urban systems [77], assessing efficiency and economic decoupling [9,91], and optimizing agricultural and productive structures under water stress [60,61,63]. Parallel developments strengthened equity-related applications, inequality reduction, and Sponge City approaches [94,95], as well as integration with carbon footprint and nature-based solutions [9]. Additional objectives included urban renewal, scarcity management, and water security [64,79,80], confirming methodological maturity in which the water footprint functions as a decision-support and policy evaluation instrument.

Overall, the temporal evolution reveals a progressive shift from diagnostic applications toward strategic, integrated, and normative roles. While efficiency, consumption, and sustainability dimensions are extensively represented, gaps persist in water justice, institutional implementation, and long-term impact assessment, indicating clear directions for future research.

4.5. Measurement of Urban Water Footprint

While the previous Section 4.2, Section 4.3 and Section 4.4 focused on dominant methodological pathways, typologies and application objectives regarding the UWF, this subsection highlights the operational core that is recurrently found in the studies reviewed in order to quantitatively measure the UWF. This involves the volumetric assessment of the amount of water that is flowing through an urban system including its various water quality aspects, and is therefore categorized into its green, blue and grey aspects. Measuring the UWF using these aspects of water is important in order to see beyond the mere volume of water flowing through an urban system and to gain a deeper and more informed understanding of the physical and environmental implications of the various water uses.

Table 4. Parameters used in the illustrative water footprint calculation.

Symbol	Parameter	Unit
${\mathit{W}\mathit{F}}_{\mathit{t}\mathit{o}\mathit{t}}$	Total water footprint	m3/t
${\mathit{W}\mathit{F}}_{\mathit{g}\mathit{r}\mathit{e}\mathit{e}\mathit{n}}$	Green water footprint	m3/t
${\mathit{W}\mathit{F}}_{\mathit{b}\mathit{l}\mathit{u}\mathit{e}}$	Blue water footprint	m3/t
${\mathit{W}\mathit{F}}_{\mathit{g}\mathit{r}\mathit{e}\mathit{y}}$	Grey water footprint	m3/t
${\mathit{C}\mathit{W}\mathit{U}}_{\mathit{g}\mathit{r}\mathit{e}\mathit{e}\mathit{n}}$	Green crop water use	m3/ha
${\mathit{C}\mathit{W}\mathit{U}}_{\mathit{b}\mathit{l}\mathit{u}\mathit{e}}$	Blue crop water use	m3/ha
$\mathit{Y}$	Yield	t/ha
${\mathit{E}\mathit{T}}_{\mathit{g}\mathit{r}\mathit{e}\mathit{e}\mathit{n}}$	Green evapotranspiration	mm
${\mathit{E}\mathit{T}}_{\mathit{b}\mathit{l}\mathit{u}\mathit{e}}$	Blue evapotranspiration	mm
$\mathit{L}$	Pollutant load	kg/ha
$\mathit{A}\mathit{R}$	Application rate	kg/ha
α	Leaching-runoff fraction	-
${\mathit{C}}_{\mathit{m}\mathit{a}\mathit{x}}$	Maximum allowable concentration	kg/m3
${\mathit{C}}_{\mathit{n}\mathit{a}\mathit{t}}$	Natural concentration	kg/m3

shows that the WF accounting requires a minimum set of crucial parameters for accurate calculation. These parameters CWU, yield and pollutant-load determine the magnitude of water footprint components. These parameters are frequently utilized in the literature to calculate the water footprint of crop, watersheds, river basins, administrative regions and products at different stages of supply chains for agricultural, regional and supply-oriented applications [53,115,116].

Following this logic, the total WF can be expressed as the sum of its three main components:

$${WF}_{tot}= {WF}_{green}+{WF}_{blue}+{WF}_{grey}$$

(1)

The total WF is treated as an additive indicator and consists of three different sources of water appropriation or water quality pressure (Equation (1)). For production-based systems, the green and blue water footprint is calculated as water use per hectare divided by grain yield:

$${WF}_{green}= {\displaystyle \frac{{CWU}_{green}}{Y}}$$

(2)

$${WF}_{blue}={\displaystyle \frac{{CWU}_{blue}}{Y}}$$

(3)

The water footprint for crop production is presented per unit of production, enabling comparisons among crops, production territories, whether domestic or abroad or production management systems (Equations (2) and (3)). Since yields among these may differ substantially, even when water use per hectares remains constant, the influence on the final footprint is considerable [117,118].

Crop water use is generally derived from accumulated evapotranspiration during the growing period, distinguishing between rainfall-derived and irrigation-derived contributions:

$${CWU}_{green}= 10\sum {ET}_{green}$$

(4)

$${CWU}_{blue}=10\sum {ET}_{blue}$$

(5)

In Equations (4) and (5) evapotranspiration is expressed in mm and converted into volumetric contents. These water consumptions can be divided into three components and reduced by the factor 10. Commonly this is done in water footprint accounting with crop water models such as CROPWAT [119] or AquaCrop [53]. The grey water footprint is calculated from the pollutant load divided by the maximum admissible increase in pollutant concentration and by the yield.

$${WF}_{grey}={\displaystyle \frac{L}{\left(C_{max}-C_{nat}\right)\ast Y}}$$

(6)

The pollutant load is frequently estimated as a fraction of the applied fertiliser:

$$L= \propto \ast AR$$

(7)

These equations link water quality issues to the water footprint concept (Equations (6) and (7)). In contrast to the green and blue water footprint components, the grey water footprint is strongly dependent on several methodological assumptions, such as the type of pollutants released, the leaching fraction, and the accepted concentration of pollutants in surface waters [120,121].

In order to strengthen the internal validation of the method, an explicit numerical example was elaborated. An agricultural production system is illustrated as linked to an urban food supply chain. The numeric values used in the calculations include: green evapotranspiration (${ET}_{green}$ = 320 mm); blue evapotranspiration (${ET}_{blue}$ = 180 mm); Crop yield = 8 t/ha; nitrogen input = 150 kg/ha; leaching coefficient (pl) = 0.10; permissible maximum concentration = 0.05 kg/m³; natural concentration = 0.01 kg/m³.

$${CWU}_{green}=10\ast 320=3200 {\mathrm{m}}^3/\mathrm{h}\mathrm{a}$$

$${CWU}_{blue}=10\ast 180=1800 {\mathrm{m}}^3/\mathrm{h}\mathrm{a}$$

$${WF}_{green}={\displaystyle \frac{3200}{8}}=400 {\mathrm{m}}^3/\mathrm{t}$$

$${WF}_{blue}={\displaystyle \frac{1800}{8}}=225 {\mathrm{m}}^3/\mathrm{t}$$

$$L=0.10\ast 150=15 \mathrm{k}\mathrm{g}/\mathrm{h}\mathrm{a}$$

$${WF}_{grey}={\displaystyle \frac{15}{\left(0.05-0.01\right)\ast 8}}={\displaystyle \frac{15}{0.32}}=46.88 {\mathrm{m}}^3/\mathrm{t}$$

$${WF}_{grey}={\displaystyle \frac{15}{\left(0.05-0.01\right)\ast 8}}={\displaystyle \frac{15}{0.32}}=46.88 {\mathrm{m}}^3/\mathrm{t}$$

The example illustrates that the final number of the water footprint also reflects the distribution of total water consumption within a production system to the three internal components of green, blue and grey water footprints. According to this distribution, the water footprint of cotton production mainly stems from consumption of rain water (59.5%), followed by consumption of irrigation water (33.5%), while the pollution burden caused by agricultural chemicals amounts to 7.0% (see Figure 8).

We then argue that this type of decomposition is particularly relevant for the UWF because by only looking at an aggregated indicator, one may miss important differences in water usage patterns embedded in apparently similar water footprints. Two systems can have the same Total WF while displaying different degrees of irrigation, rainfed, or pollution-intensive water use. To maximize the analytical value of WFA, it is therefore fundamental to decompose total water footprint to interpret its results meaningfully [122,123,124].

Reporting total or partially aggregated WF values is often reported in studies on UWF without clarifying key assumptions, parameters and sectoral contributions. Building on such approach it is important to provide a transparent methodology based on the Equations (1)–(7), in conjunction with the parameters’ definition presented in Table 4. Such an approach will pave the way from a descriptive accounting to planning-oriented analyses; the transparency in measuring UWF is especially significant for interpreting urban water pressure, i.e., to distinguish whether such pressure is primarily caused by blue-water abstraction in the region studied, by external rainfed productions, or by pollution embedded in supply chains. In summary, transparency in measuring UWF is essential and therefore should be considered as a basic requirement for practical applications.

Nevertheless, transparency in volumetric measurement does not, by itself, indicate the severity of water-related impacts. A cubic meter of blue water consumed in a water-abundant basin cannot be interpreted in the same way as a cubic meter consumed in a water-scarce basin. For this reason, volumetric decomposition should be understood as a necessary analytical step in UWFA, but not as a substitute for scarcity-weighted or impact-based interpretation. When the aim is to evaluate environmental pressure, water stress, or policy priorities across different urban contexts, volumetric indicators need to be complemented by methods capable of incorporating hydrological scarcity, local vulnerability, and basin-specific impact conditions.

5. Discussion

5.1. Structural Gaps (RQ5)

The predominance of single-city studies constitutes a relevant structural feature of current UWF research. This scale is consistent with the central purpose of UWFA, since the city remains the main operational unit for diagnosing urban water use, pollution pressures, infrastructure performance, and planning needs. However, treating the city as a closed analytical unit may limit the interpretation of water pressures that are generated beyond municipal boundaries but are ultimately driven by urban consumption, production, and service demands. In this sense, city-region, multi-city, and supply-chain perspectives should not replace the city-centred focus of UWF studies, but rather complement it by making visible upstream dependencies, downstream effects, virtual water flows, and displaced water pressures associated with urban systems. Strengthening this complementary perspective would allow UWF research to preserve its urban focus while better representing the multiscalar and interconnected nature of city water metabolism.

Urban metabolism and structure constitute key elements of the present-day urban production system and its environmental implications. These elements are not yet sufficiently addressed in the context of urban sustainability and ecosystem services, which constitute less than 30% of the Cited Reference Search core [70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86]. Many aspects of contemporary urban production, such as high water footprint and contamination, are closely linked to these aspects. An imbalance between them is reported in the scientific literature, which may be due to the water footprint’s widespread use as a summary indicator to assess the environmental impacts of urban production systems. In contrast, its potential to break down the relationships among production, governance, and distribution in the urban metabolism and structure has not yet been fully explored.

5.2. Methodological Implications

The identified structural gaps are directly reflected in the methodological landscape. Taking the frameworks from the literature as a reference, 57.14% of the literature determined the methods of WF accounting [6,8,9,60,61,62,63,64,65,76,77,78,79,80,91,92,93,94,95,101,102,103,104,105]. Using standardized indicator data, the quantitative comparison of the elements of the urban metabolic system is achieved. However, the static structure of the framework cannot reflect the dynamic changes in the system’s structure, the feedback among the elements of the urban ecosystem, or the evolution over time.

Although volumetric water footprint accounting provides a transparent and comparable basis for describing direct and indirect water appropriation in urban systems, its interpretation requires caution. This approach is particularly useful when the purpose is to quantify the magnitude and composition of water use, distinguish between green, blue and grey components, identify virtual water dependencies, or compare the internal structure of urban water demand. However, volumetric values should not be interpreted automatically as equivalent to environmental impact or water stress. The same volume of water may have substantially different implications depending on basin-level scarcity, seasonal availability, environmental flow requirements, water quality thresholds, and the ecological sensitivity of the source region. In this sense, volumetric UWFA is most robust when used as a diagnostic and accounting tool, but it may become misleading if it is used alone to rank sustainability performance across cities located in contrasting hydrological contexts. Therefore, future studies should complement volumetric WF estimates with scarcity-weighted indicators or impact-based LCA metrics, particularly when the objective is to assess environmental damage, prioritise interventions, or support policy decisions. Such integration would make it possible to distinguish more clearly between water appropriation as a physical flow and water-related impact as a context-dependent environmental pressure.

System-boundary consistency is therefore a central methodological challenge in UWF research. In accounting-based studies, boundaries are often defined around the administrative city, whereas MRIO and hybrid approaches usually extend the analysis to upstream production systems and interregional supply chains. This difference improves the capacity to capture virtual water dependencies, but it also increases the risk of sectoral overlap and double counting if direct municipal water use, intermediate production inputs, and final consumption flows are not clearly distinguished. For this reason, future UWFA should explicitly report whether upstream and downstream flows are included, how sectors are allocated, and how overlaps between direct and indirect water uses are avoided.

Compared to LCA, the IO/MRIO models [4,71,85,87,88,91,92,96,97,98,107] and the de-composition-based methods [62,67,74,81,95,106,110,114] are seen as providing additional information at the level of virtual flows, agents of change and of the distribution of the responsibility of the unintended effects of production and consumption activities. Even if these models are not extensively used in the literature, the available applications span different spatial scales and governance levels and therefore do not yet address the suburban scale or planning tools. The hybrid models that integrate the LCA approach with the ecological footprint [63,68,72,111] represent an evolution of the analysis of the systemic effects of the consumption patterns, but also require more research in this field, which is currently more based on empirical applications rather than on the development of innovative methods. Finally, network and spatial analyses represent emerging approaches [52,90] and their use for the analysis of urban resilience and metropolitan resilience and connectivity is still under development.

5.3. Comparative Methodological Guidance: Volumetric WF, LCA and Hybrid Approaches

The comparison between volumetric WF accounting and LCA-based approaches is central for clarifying methodological selection in UWF research. Volumetric WF accounting estimates the physical amount of green, blue, and grey water associated with direct use, production processes, or consumption patterns. Its main strength lies in its transparency, relative simplicity, and capacity to describe the structure of water appropriation across sectors and urban systems. For this reason, it is particularly suitable for diagnostic assessments, decomposition of WF components, identification of virtual water dependencies, and comparison of water-use profiles within a clearly defined system boundary. However, as discussed above, volumetric WF does not necessarily represent environmental impact, since it does not fully account for local scarcity, ecosystem vulnerability, seasonal variation, or basin-specific response conditions.

In contrast, LCA-based water footprint methods are more appropriate when the objective is to evaluate potential environmental impacts associated with water use throughout a product, service, infrastructure system, or urban supply chain [1,34,37,38]. Their main advantage is that they can incorporate impact pathways and scarcity-weighted characterisation factors, allowing water consumption to be interpreted in relation to regional water stress and environmental consequences. Nevertheless, LCA-based approaches often require more detailed inventory data, methodological assumptions, and impact models, which may limit their application in cities where data availability is fragmented or where informal, indirect, and cross-boundary water flows are difficult to trace.

Hybrid approaches offer a promising pathway for overcoming the limitations of using either framework in isolation. By combining volumetric WF accounting with LCA, MRIO, decomposition analysis, ecological footprint approaches, or spatial methods, hybrid frameworks can connect physical water appropriation with supply-chain dependencies, impact interpretation, and urban planning relevance [63,68,72,111]. Therefore, methodological selection should depend on the purpose of the assessment. Volumetric WF is most appropriate for accounting, benchmarking, and identifying the composition of water use; LCA-based metrics are preferable for impact-oriented comparisons and sustainability assessment; and hybrid approaches are especially relevant when the objective is to analyse complex urban systems, cross-boundary flows, policy scenarios, and integrated water–energy–food or urban metabolism relationships.

To synthesise this methodological guidance,

Table 5. Comparative guidance for selecting methodological approaches in UWFA.

Approach	Best Suited for	Main Caution	Urban Use
Volumetric WF accounting	Quantifying green, blue, grey, or Total WF and decomposing water-use structure.	Does not directly indicate impact, scarcity, or basin sensitivity.	Diagnosis, benchmarking, WF decomposition, virtual water identification.
Scarcity-weighted WF	Comparing water pressure across cities, basins, or supply areas.	Depends on reliable scarcity factors and spatial/temporal resolution.	Prioritising action in water-stressed urban systems.
Impact-based LCA metrics	Assessing environmental impacts of products, services, infrastructure, or supply chains.	Requires detailed inventories and characterisation factors.	Comparing planning, infrastructure, and consumption alternatives.
Hybrid approaches	Integrating accounting, supply chains, impacts, and policy relevance.	Requires clear boundaries to avoid overlap or double counting.	Urban planning, governance scenarios, WEF nexus, urban metabolism.

summarizes the main conditions under which each approach is most appropriate, its principal limitations, and its potential use in UWFA.

5.4. Policy and Planning Relevance

Although a relevant portion of the corpus explicitly addresses urban policy and governance [4,9,92,93,94,95,96,97,98,99,100], the translation of water footprint results into regulatory instruments, compensation mechanisms, or integrated planning strategies remains limited. In many cases, the water footprint functions as an early-warning or diagnostic indicator rather than as an operational decision-support tool. Nevertheless, UWFA can support planning and governance practice in several concrete ways. First, it can identify hotspots of direct and indirect water use, allowing local governments to prioritize sectors, activities, or consumption patterns with the highest pressure on freshwater resources. Second, it can inform urban planning decisions by linking water demand, pollution loads, land-use change, green infrastructure, urban renewal, and water-sensitive design strategies [52,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90]. Third, when combined with governance-oriented approaches, UWF results can support policy instruments related to demand management, wastewater reuse, water efficiency standards, urban food systems, public procurement, and intersectoral water allocation.

From a governance perspective, UWFA is particularly valuable because it makes visible water pressures that are not always captured by conventional urban water statistics. These include virtual water embedded in goods and services consumed in cities, pollution-related grey water pressures, and dependencies on external basins or production systems. In this sense, UWF can contribute to sustainability transitions by helping cities move from infrastructure-centred water management toward integrated strategies that connect consumption, production, planning, environmental quality, and social equity. However, this potential requires stronger integration between UWF indicators and institutional decision-making frameworks. Without such integration, the water footprint may remain mainly descriptive, limiting its capacity to guide transformative urban water governance.

5.5. Practical Implications for Urban Water Management

The findings of this review have practical implications for urban planners, water utilities, environmental authorities, and policy-makers. First, UWFA can help identify the sectors, activities, and consumption patterns that generate the highest direct and indirect water pressures, allowing decision-makers to prioritise interventions in areas such as demand management, wastewater reuse, pollution control, green infrastructure, and water-efficient urban design. Second, by distinguishing between green, blue, grey, and Total WF components, UWF analysis can support more targeted strategies, differentiating whether urban water pressure is mainly associated with local abstraction, external resource dependence, or pollution-related impacts.

Concrete planning and governance applications can be derived from these findings. For instance, when grey WF dominates the urban profile, UWF results can support decisions related to wastewater reuse, pollution-load reduction, and stricter control of discharge standards. When blue WF or external virtual water dependencies are dominant, the results can inform demand-management policies, water-efficiency standards, public procurement strategies, and urban food-system planning. Similarly, in urban renewal or Sponge City contexts, UWFA can help compare planning alternatives by identifying whether proposed interventions reduce local abstraction, pollution pressure, or externalised water dependence.

In practical terms, UWF should not be used only as a descriptive indicator, but as an input for integrated urban water governance. When combined with scarcity-weighted indicators, LCA-based metrics, MRIO models, or spatial analysis, UWF can inform planning decisions related to urban renewal, public procurement, food-system policies, industrial allocation, and sustainability transitions. This is particularly relevant for cities seeking to reduce hidden water dependencies, align infrastructure planning with environmental limits, and connect water management with broader objectives of resilience, equity, and sustainable urban development.

6. Future Research Agenda

Based on the identified gaps, several priority research directions emerge for advancing water-sustainable urban systems: (i) Multiscalar analysis for understanding urban spatial linkages and footprint transfers from city-region to multi-city systems as well as from the interior to the periphery of cities [52,71,72,73,75,81,87,88,89,99,100,111,113,114]. (ii) Neighborhood-level analysis and urban water equity [90,103].

Future research should elaborate on the relationships between urban metabolism and industrial structure in greater depth, taking into account the productive sector and urban value chains to better understand the effects on water scarcity [91,112]. Finally, an integrated methodological framework that combines MRIO, decomposition analysis, spatial analysis, and governance perspectives is required to move from the descriptive and analytical characterisation of the current status of water scarcity to predictive and transformative policy-making tools.

Conclusion regarding RQ5, as discussed in the previous sections, there are many conceptual, methodological and spatial challenges associated with the research of UWF. While significant progress has been made in quantifying urban water consumption and pollution in the literature, many studies remain one-sided, focusing solely on physical characteristics, while neglecting the social and institutional dimensions captured by accounting principles. In addition, the omission of the neighbourhood scale, multi-city systems, and perspectives related to urban metabolism and governance remains substantial, thereby reducing the transformative power of the water footprint approach. Therefore, the water footprint approach needs to evolve towards more holistic and integrated approaches to assess urban water forms and structures, as well as urban water-related planning and policy-making processes, and to design water-efficient planning tools for water-sustainable cities.

7. Conclusions

Over the last few years, UWF has become one of the key parameters explaining the pressure exerted on the urban water system, particularly in more complex, interdependent, and fragile urban systems. This research presents the current state of knowledge on UWF, focusing on conceptual developments, methodologies, and applications in urban water systems over the last 20 years. This work is therefore based on a systematic review protocol prepared in accordance with the PRISMA guidelines, and on the quality assessment procedure in accordance with the Kitchenham and Charters method. The final reliable analysis found 61 papers.

Results indicate a sustained expansion of the field, characterised by a transition from exploratory assessments to applications oriented toward urban planning, governance, and sustainability (RQ1). The methodological analysis reveals a strong reliance on water footprint accounting approaches, accompanied by progressive diversification toward MRIO, decomposition, and hybrid frameworks, although clear asymmetries remain in complexity and scalability (RQ2). Spatially, single-city analyses dominate, while multi-city, metropolitan, and global assessments remain limited, constraining the understanding of territorial interdependencies and virtual water transfers (RQ3). Application purposes evolve from conceptual comparisons to agendas focused on efficiency, consumption, diet, resilience, and urban policy, although certain social and equity dimensions remain underrepresented (RQ4). These patterns reveal persistent structural, methodological, and geographical gaps, particularly in Global South contexts, intermediate spatial scales, and integrated governance approaches (RQ5).

The main contribution of this review lies in providing an integrated analytical synthesis of UWF research that connects methodological approaches, water footprint typologies, spatial scales, urban-system boundaries, and application objectives within a single interpretative framework. Unlike studies focused only on general water footprint methods or sector-specific applications, this review specifically systematizes how UWF has been operationalized in urban contexts and identifies the conditions under which it can support planning, governance, and sustainability-oriented decision-making. In doing so, the study offers a structured basis for improving methodological comparability, clarifying system-boundary assumptions, and guiding future UWFA.

In synthesis, the research highlights the need for a multiscale and transdisciplinary strategy to advance towards water-sustainable urban systems and to better integrate WFA with urban planning and decision-making processes. The research results provide a strong basis for future research, enhancing comparability and informing urban planning decisions.