The visible crisis

Throughout history, most cities were established in areas with ample freshwater to meet their residents’ needs. Continued city growth, exacerbated by climate change, is making urban water management harder, however. Cities are confronting unprecedented hydrologic changes due to global climate change. This affects not only the spatial and temporal availability of water but can also cause damage to existing urban water infrastructure, deteriorate surface water quality, and pose serious threats to current operating models of urban water management [1]. By one estimate, between one third and half of the world’s urban population will face water scarcity in the year 2050 [2].

Cities’ water sources are also threatened by contamination with solid waste and domestic wastewater generated by households [3]. Currently, only about half of all urban wastewater flows are collected and safely treated before being discharged to the environment. A host of other contaminants, including industrial chemicals, agricultural fertilizers, microplastics, and sediments are discharged to urban water bodies through multiple contamination pathways, impairing water quality significantly more than previously estimated [4]. Exposure to pollutants is highest, and access to water and sanitation services lowest, among populations who are marginalised because of income, disability, gender, religion and other characteristics. These inequities in turn lead to disparities in health, economic and social outcomes [5].

Such challenges confront cities in every world region and across the entire economic spectrum. This set of PLOS Water articles—and others that will be added to the collection in coming months—helps to deepen our collective understanding of those challenges. It also provides an opportunity to learn from novel approaches and lighthouse initiatives around the world that are transforming planning, management and monitoring of both watersheds and water and sanitation service delivery systems in urban areas. From the diverse array of topics addressed by the papers’ authors, a handful of themes emerged as worthy research priorities for the urban water community.

Inequality

Cities are spatially and demographically heterogenous, which has impacts on the water security of individual neighbourhoods and areas. Victor et al. investigate this intra-urban spatial heterogeneity within an informal settlement in Beira, Mozambique, and how it relates to residents’ access to water supply and sanitation services [6]. Their analysis shows key determinants of water access and corresponding satisfaction with service, including distance from water main.

Tomko et al., explored differences in the responses of public water services to the Winter Storm Uri in Texas [7]. They observed various disparities in the disruption length and related boiled water advisories for urban and rural communities varying in size and socioeconomic status. Turley on the other hand studied the water allocation patterns between urban and rural areas in three countries. They critique the increased urban water allocation using financial power and the inequitable intra-urban allocation that followed [8].

At the household level, Huberts et al., provide a fine-grained analysis of the monetary and non-monetary costs of ‘converting intermittency to continuity’, i.e., how users cope with intermittent water supply through adaptations to household-level water infrastructure and labour practices [9]. They combine survey, interviews and ethnographic data from Mexico City to discuss the consequences of these costs on the inequalities caused due to uneven water distribution. Genter et al., analysed household self-supply and its associated motivations and management practices in urban Indonesia [10]. The study offers insights on use preference of self-supply and its supplementation using alternate water sources including public piped system. It also shows the intra-household dynamics of gendered cooperation in clearly defined roles for men and women.

Inclusive governance

Trimmer et al., characterises the enabling environment for equitable access to safe drinking water using six cities across three continents as successful case studies [11]. This adds to the growing literature on enabling environment for water and sanitation services by providing clear entry points to improvements for different typologies of service provision. One aspect of such an enabling environment is community involvement in planning and management of water and sanitation services. Catherine et al. follow suit in understanding community perceptions on quality and safety of drinking water in Mbarara city, Uganda [12]. They raise the possibility that community appraisal could contribute to the monitoring of water service quality.

Public health

Water and sanitation are foundational pillars of public health, reducing exposure to fecal pathogens especially in densely populated urban areas. Two articles of this collection explore patterns of fecal contamination and their associated health risks in Africa. Using the established SaniPath assessment tool Coulibaly et al. estimate the faecal contamination exposure from soil, street food, flood water, drinking water, gully water and open drain water for residents of an Abidjan, Côte d’Ivoire suburb [13]. They find evidence of fecal contamination in 90% of the 120 environmental samples collected, as well as higher rates of estimated exposure among children compared to adults. In Lusaka, Zambia Gething et al. employ geospatial analysis to estimate cholera risk under a range of water and sanitation infrastructure investment scenarios, using available epidemiological, economic and demographic data [14]. The results are being used to inform decision-making, and the approach could be adapted to other contexts.

Karimi et al. report contamination of 14% of the wells they tested in informal settlements of Kisumu, Kenya with the antibiotic combination of sulfamethoxazole and trimethoprim. Antibiotics are another class of emerging water contaminants of growing concern because they are being detected in groundwater worldwide and have a hypothesized role in antibiotic resistance [15]. Informal settlements are often the setting of a negative spiral—low access to sanitation causing high rates of infectious disease, leading to increased use of antibiotics, ultimately contributing to greater resistance to antibiotics in the disease-causing microbes. Together, the three studies reinforce the importance of incorporating public health considerations into planning water supply and sanitation services.

Approaches to urban water resource management

Three papers in the collection bring a basin-scale perspective to urban water scholarship. Kammoun et al., focus on water resource protection of a combined urban and agriculture watershed in Quebec, Canada [16]. Using a Bayesian model, they estimate the risk of water supply contamination from agricultural run-off, contributing a water quality piece to an integrated water resource management puzzle. Talib and Randhir study the effects of land use changes, especially urbanisation, on the hydrology and water quality in the Sudbury-Assabet and Concord watershed of Massachusetts, U.S.A. [17]. Their model shows that an increase in impervious area and decrease in forest area are causing an increase in urban stormwater run-off, with significant impacts for water quality, especially on sediment and nutrient loading.

In cities around the world the frequency and magnitude of flooding are increasing as a result of a changing climate and urbanisation, giving rise to the need for new management and planning strategies [18]. Michaels presents an innovative and inclusive governance approach employed with two infrastructure projects in Lincoln, Nebraska, U.S.A. Both projects tackled multiple goals while prioritising urban flood management [19]. The governance approach created context-specific administrative coordination mechanisms that traverse jurisdictions, allowing for more effective watershed-scale resource management.

Conclusion

This collection highlights the importance of, and progress toward, developing sustainable and equitable solutions to urban water management challenges. The inclusion of research from a variety of contexts helps identify the conditions under which particular tools and approaches are more (and less) likely to be effective. Taken together, the articles demonstrate the value of inter- and trans-disciplinary perspectives in conceiving, testing, and pursuing transformative urban water management ideas. The research included in this collection makes important contributions to help advance safe and sustainable water resources management and water supply and sanitation service delivery in cities that face an increasingly complex set of environmental, human health, and equity challenges.