Environ. Res. Lett. 13 (2018) 053002 https://doi.org/10.1088/1748-9326/aaba52

TOPICAL REVIEW

Urban water security: A review

Arjen Y Hoekstra1,2,4 , Joost Buurman2 and Kees C H van Ginkel1,3

1 Twente Water Centre, University of Twente, Enschede, the Netherlands2 Institute of Water Policy, Lee Kuan Yew School of Public Policy, National University of Singapore, Singapore3 Deltares, Delft, the Netherlands4 Author to whom any correspondence should be addressed.

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E-mail: a.y.hoekstra@utwente.nl

Keywords: urban water management, sustainability, adaptation, resilience, external water dependency

AbstractWe review the increasing body of research on urban water security. First, we reflect on the fourdifferent focusses in water security literature: welfare, equity, sustainability and water-related risks.Second, we make an inventory of the multiple perspectives on urban water security: disciplinaryperspectives (e.g. engineering, environmental, public policy, public health), problem-orientedperspectives (e.g. water shortage, flooding, water pollution), goal-oriented perspectives (e.g. betterwater supply and sanitation, better sewerage and wastewater treatment, safety from flooding, properurban drainage), integrated-water versus water-integrated perspectives, and policy analytical versusgovernance perspectives. Third, we take a systems perspective on urban water security, taking thepressure-state-impact-response structure as an analytical framework and link that to the ‘urban watertransitions framework’ as proposed by Brown et al (Water. Sci. Technol. 59 2009). A systemsapproach can be helpful to comprehend the complexity of the urban system, including its relationwith its (global) environment, and better understand the dynamics of urban water security. Finally,we reflect on work done in the area of urban water security indices.

1. Introduction

Researchers, policy makers and business leadersincreasingly talk aboutwater security.Apparently, thereis something at stake. The concept of water securityis used from the household to the global level. Inthis paper, we focus on water security at the urbanlevel. But first something about the concept in gen-eral. The term water security is fashionable, fitting inthe current time spirit with its focus on all sorts ofsecurity issues, so one may wonder whether it is oldwine in a new bottle (Lautze and Manthrithilake 2012).Indeed, it seems that a lot of writings that previouslywent under headings such as integrated and sustainablewater management now go under this new headingof water security. At the same time, however, thechanging terminologies over time also reflect chang-ing insights and changing focusses. Halfway throughthe 1980s, scholars increasingly spoke of integratedwater (resources) management (figure 1), to highlightconcerns that water problems could not be properlyaddressed if not taking a more holistic approach. Itbecame clear that water systems had to be considered

as a whole, since surface water and groundwaterresources are linked, as are water quantity and waterquality issues. Besides, it was acknowledged that watersystems fulfil different functions, all to be considered inan integrated analysis. From around 1990 the term sus-tainable water (resources) management became ratherpopular as well, inspired by the successful uptake ofthe idea of sustainable development after the publi-cation of the Brundtland report. A decade ago, theterm adaptive water management became increasinglypopular, inspired by the need to ‘adapt’ to climatechange, but the term soon became used in a muchbroader way, referring to the need to continuouslyadapt to and flexibly respond to changing circum-stances in general (Pahl-Wostl 2007). Other terms thathave become increasingly popular recently are waterrisk, water resilience, water proof, and the water-food-energy nexus. Water security, however, is a term takinga central position. The term has got off the ground sincearound 2000, with the publication of A Water SecureWorld by the World Water Council (WWC 2000) andTowards Water Security: A Framework for Action bythe Global Water Partnership (GWP 2000). Although

© 2018 The Author(s). Published by IOP Publishing Ltd

Environ. Res. Lett. 13 (2018) 053002 Arjen Y Hoekstra et al

Figure 1. Emergence of new water management concepts over time.

the word security suggests a certain focus, in practicethe term water security is generally taken so broadthat it captures all that also goes under headings likeintegrated, sustainable and adaptive.

The concept of urban water security is differ-ent from the more general water security concept inits application to the territory of an urban area, amunicipality orurbanagglomeration.This introduces anumber of elements that are specifically valid for urbanwater security, and not for water security at household,state, country or global level. The essence of an urbanarea is its high population density and dependence onits hinterland for the supply of its natural resources.For water this means that large urban areas are gen-erally incapable of meeting their water supply fromwithin the urban area itself. This is solved by supplyingwater resources fromoutside, sometimes fromfar away.McDonald et al (2014) call this the ‘reachof urbanwaterinfrastructure’. Urban areas depend even more onwater resources elsewhere for producing the food con-sumed by the urban citizens. This has been describedas the ‘external water footprint’ of urban consumption(Hoekstra et al 2011, Hoff et al 2014). Since there arerisks attached to such dependency, we speak here aboutthe ‘imported urban water risk’. This dependence onexternal water resources, through both water transfersfor urbanwater supply and food imports for urban foodsupply, is an inherent and typical concern for watersecurity at the urban level. In addition, the high densityof people and economic activities in urban areas con-centrates risks. This requires relatively high protectionstandards and sometimes different risk managementapproaches. Urban water security further differs fromwater security at other levels in the typical governancesetting at this level, with different municipality depart-ments responsible for distinctive water-related tasksor for tasks indirectly relevant (like spatial planning),with municipal policies but national regulations as well,with a public or private water supply utility and otherpolicy processes and stakeholders typical to the urbanlevel. Just like in the case of the water security con-cept in general, at the urban level there are variousoverlappingandcompeting termsused: integrated, sus-tainable and adaptive urban water management, urbanwater resilience, and water- and climate-proof cities.

The goal of this paper is to review the litera-ture on urban water security. We have identified themost relevant scientific literature in Web of Science

using the key words ‘water security’, ‘urban watersecurity’, ‘urban water management’, ‘urban watersustainability’, ‘urban water resilience’, ‘urban watervulnerability’ and ‘urban water risk’, supplementedwith an online search for urban water security and sus-tainability indicators and indices. In this review, wefirst reflect on the different interpretations of watersecurity. Second, we make an inventory of the multipleperspectives on urban water security. Several authorshave highlighted the multitude of relevant approachesbefore (e.g.Cook andBakker2012, vanBeek andLinck-laen Arriens 2014), but by putting it all together weget a more comprehensive overview than in earliercontributions. Third, we take a systems perspectiveon urban water security, using the pressure-state-impact-response structure as an analytical framework,and link that to the ‘urban water transitionsframework’ as proposed by Brown et al (2009).Finally, we reflect on work done in the area of urbanwater security indices.

2. What is water security?

The Global Water Partnership considers water securityas the overarching goal of water management (GWP2000). People, however, obviously differ in what theysee as the goal. One may thus expect different defi-nitions of water security. Besides, not everyone mayagree on water security as the encompassing con-cept to reflect the overall goal of water management;some prefer to attach a narrower meaning to this con-cept and use it along with other concepts of equal oreven greater importance. In the literature, we observefour different focusses when researchers define andstudy water security: it is about using water suchthat we are increasing economic welfare, enhancingsocial equity, moving towards long-term sustainabil-ity or reducing water-related risks (figure 2). Scholarsoften combine these points of view to different extents,but distinguishing the four interpretations helps tounderstand why treatments of urban water securityoften appear to be so different.

A focus on welfare seems all encompassing: thereason to care for an optimal water system and thebest fulfilment of the various functions and servicesof the water system in an urban area is that this con-tributes to increasing urban welfare. Particularly when

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Figure 2. Different focusses in the definition and study of water security.

we interpret ‘welfare’ in broad terms, including eco-logical and social values and risks, the essence of watersecurity boils down to increasing welfare for all in thelong term. The value of different water system services(e.g. water supply, flood protection, green water cor-ridors) could be measured in terms of their relativecontribution to urban welfare. From this perspective,enhancing ‘urban water security’ more or less comesdown to increasing the benefits from water in the city,as well as reducing or avoiding damage associated withwater in the city. There is something to say for this,because welfare is an overall measure of development,but it can easily simplify the concept to an unaccept-able level. Aesthetic, cultural and ecological values ofwater are difficult to capture in the (economic) ter-minology of welfare, and how benefits are distributedamongcitizens is generally not caught in anoverallmet-ric of welfare. This is not unimportant, because waterinsecurity often concerns particular groups, which mayeven be the essence of the whole concern about watersecurity: that it does not reach all in society. It isthe poor in a city that do not have access to properdrinking water supply and sanitation; the rich in thesame city are perfectly fine. Another problem withmeasuring water security in terms of its contributionto welfare is the time dimension: water insecurity isnot necessarily visible today, it may lie in processesthat play out in the long term: continued urbaniza-tion in low-lying areas in the world, sea-level rise, landsubsidence due to groundwater pumping, increasingfrequency of extreme events like rains and river flowsfrom upstream causing flooding, and increasing waterdemands while water availability is limited. The waywelfare theoretic concepts deal with intergenerationaltransfers—the welfare of future generations—throughdiscount rates is hotly debated (Goulder and Williams2012). Finally, properly including risks in welfare met-rics is known to be difficult, particularly given the factthat risks often include large uncertainties that are dif-ficult to quantify but form part of the essence of waterinsecurity.

When the welfare focus is expanded to includeequity and sustainability as well, van Beek and Linck-laen Arriens (2014) call this the ‘development focus’on water security, which in their view then con-trasts with the risk focus on water security. In thebroader developmental approach, water security issomething to improve over time, with certain goalsand targets and a combination of policies, reforms, and

investment projects to achieve those goals. Thisapproach captures three of the four focusses men-tioned: growth in welfare, equity and sustainability.The risk-based approach centres around the fourthfocus: managing risks and reducing vulnerability toshocks from climate variability and water-related disas-ters. Van Beek and Lincklaen Arriens (2014) argue thatthese two approaches are complementary, and needto be pursued simultaneously and in a balanced man-ner. Many scholars, however, interpret water securitynarrower. Among those scholars that take a develop-mental approach to water security we see that somefocus more on economic growth (Sadoff et al 2015),while others focus on the equitable distribution ofwater values across individuals (Zeitoun 2011) and yetothers on the sustainability of water management (Bog-ardi et al 2012). Grey et al (2013) take the exclusiverisk standpoint by defining water security as a tolera-ble level of water-related risk to society. According toHall and Borgomeo (2013), this focus on water risksis congruent with the language of ‘security’ and bringstheoretic, empirical and operational substance to theterm ‘water security’. They argue that the risk approachallows the estimation of the effectiveness of investmentof resources in reducing water-related risks in terms oftheir marginal benefit. The downside of this approach,which is grounded primarily in engineering and eco-nomic traditions, is that it tends to oversimplify byrepresenting uncertainties through calculable risks andthusunderplaydiversity andpolitics in society (Zeitounet al 2016). The risk approach easily comes down to acost-benefit analysis at macro-economic level with amain focus on overall welfare, with an undervaluationof issues of equity and sustainability, values that aredifficult to quantify, and uncertainties. A more holisticapproach to water security is taken by GWP (2012),which describes a water secure world as one in which‘there is enough water for social and economic devel-opment and for ecosystems. It integrates a concernfor the intrinsic value of water together with its fullrange of uses for human survival and well-being. Itharnesses water’s productive power and minimises itsdestructive force. It is a world where every person hasenough safe, affordable water to lead a clean, healthyand productive life. It is a world where communitiesare protected from floods, droughts, landslides, ero-sion and water-borne diseases.’ According to GWP(2012), water security further means ‘addressing envi-ronmental protection and the negative effects of poor

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Figure 3. Hazard-exposure versus vulnerability.

management, which will become more challenging asclimatic variability increases. A water secure worldreduces poverty, advances education, and increases liv-ing standards. It is a world where there is an improvedqualityof life forall, especially for themost vulnerable—usually women and children—who benefit most fromgood water governance.’ Such a lengthy description ofwhat water security encompasses definitely increasesthe chance that nothing important is left out, but at thesame time of course it excludes clarity about trade-offsthat will need to be made. In this sense, it is rathera concept that brings people together to start a dis-cussion about important issues around water than awell-defined measurable concept.

Regarding water security from a risk viewpoint, afew additional remarks are to be made. Risk is a combi-nation of hazard, exposure and vulnerability (Garrickand Hall 2014). Possible hazards include, for exam-ple, drought, flooding, and water quality deterioration.Exposure is always relatively high in urban areas due tothe concentration of people and assets. A city may bevulnerable because of ill-preparedness, while anothercity facing the same hazards may be much less vulner-able because of proper adaptation, sufficient copingcapacity and measures to increase resilience. Citiesfacing relatively low water hazard-exposure, may stillhave high vulnerability due to, for instance, poor waterinfrastructure. Two cities may have a similar overall‘risk’ or ‘security’ but differ in terms of the underly-ing factors: low hazard-exposure may come with highvulnerability (e.g. bad infrastructure, bad governance),while high hazard-exposure may come with low vul-nerability (well-preparedness). These situations mayresult in similar ‘overall’ risk or security levels, but theyare fundamentally different. In the one case, the natu-ral conditions may be quite good while risks increasedue to inappropriate management, leading for exam-ple to water pollution and sub-optimal water supply.In the other case, the natural conditions may pose allsorts of challenges, like water shortages and floods,while proper management reduces risk. For this rea-son, it will always be essential to explicitly distinguishbetween hazard-exposure and vulnerability underly-ing a certain overall risk level (figure 3). An exampleof relatively low hazard-exposure combined with low

vulnerability is Toronto, a city with a moderate con-tinental climate with monthly rainfall constant overthe year. Lake Ontario provides a very large freshwaterbuffer, although it also gives some storm surge haz-ard. The combination of high hazard-exposure andlow vulnerability is probably valid for Dubai, whichhas a hot desert climate, very little rainfall and hardlyany freshwater resources. However, the big wealth ofthe city enables the government to fulfil the enormousfreshwater demand by energy consuming desalina-tion technologies. Less preparedness exists though forincidental rain showers. Another, but very differentexample of high hazard-exposure but low vulnerabilityis Amsterdam, which faces a substantial flood hazard,resulting from its elevation at around sea level in com-bination with the occurrence of large storm surges atthe North Sea. However, the very high standard offlood protection infrastructure provides that floodinghas not occurred in recent history. The opposite oflow hazard-exposure but high vulnerability is found inSao Paulo, which, with 1400 mm y−1, receives a largeamount of rainfall annually. The water demand in thismetropolis is very high, but the surrounding basinstheoretically offer sufficient water to supply the city;poor infrastructure and management, however, resultsin regular water shortages, and water pollution in thecity is considerable as well. Finally, the combinationof high hazard-exposure and high vulnerability canbe found in Jakarta. Located in a low-lying, subsid-ing delta and challenged by heavy monsoon rains, thecity is threatened by a substantial flood risk. The city isvery large, not wealthy and has a lot of slums. Althoughthe area is water-abundant, the groundwater resourcesare heavily overexploited and the quality of fresh-water resources is severely deteriorated. Riverine andstorm water flooding is occurring on a yearly basis.

3. Multiple perspectives on urban watersecurity

3.1. Disciplinary perspectivesScientists from different disciplinary backgroundsappear to give different interpretations to the termwater security. Cook and Bakker (2012) discuss

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Figure 4. Multiple perspectives on urban water security.

framings of water security across the physical and socialsciences. They find that in the engineering domain,water security studies generally focus on protectionagainst water related hazards (floods, droughts, con-tamination, and terrorism) and water supply security(percentage of demand satisfied). Water resourcesstudies rather focus on water scarcity, and water sup-ply and demand management. Environmental studiesgenerally focus on the access to water functions andservices for humans and the environment, on wateravailability in terms of quality and quantity, and onminimizing impacts of hydrological variability. Pol-icy studies focus on interdisciplinary linkages (food,climate, energy, economy and human security), pro-tection against water-related hazards, and sustainabledevelopment of water resources to ensure access towater functions and services. Public health studiesput emphasis on supply security and access to safewater, and prevention and assessment of contamina-tion of water in distribution systems. We can addto this the political perspective focusing on powerstructures, equity issues and conflicts over water, thegovernance perspective focusing on planning, institu-tional arrangements and divisionof responsibilities, thelegal perspective focusing on water rights and owner-ship, and the economic perspective focussing on theefficiency of water resources use, the economics ofwater demand and supply, water pricing and marketmechanisms, cost-benefit analysis of flood risk pro-tection and water quality conservation, valuation ofenvironmental services of water systems, and internal-ization of externalities (figure 4). Cook and Bakker(2012) observe that different disciplines also tend toanalyse at different scales: whereas development stud-ies often consider the national scale, hydrologic studiesgenerally employ a catchment scale, and social sci-entific studies usually focus on the community scale.Recognizing the multiple disciplinary perspectives andmultiple spatial scales involved, the 2013 Bonn Dec-laration on Global Water Security (GWSP 2013) callsfor a renewed commitment to adopt a multi-scale andinterdisciplinary approach to water science. Interest-ingly though, the declaration is highly water-centric,calling to address water challenges through a broadwater agenda and innovation in water institutions. Atrue interdisciplinary approach should allow for a

much wider array of perspectives, recognizing thatwater security is intricately linked to human devel-opment, governance in broader sense than ‘watergovernance’, food and energy security, social equity,and environmental sustainability.

3.2. Problem-oriented perspectivesUrban water issues can be summarised as ‘too little,too much, too dirty’. Underneath this simplificationlies a myriad of complex and interrelated problemsand challenges. Urban areas have very high levelsof human interference in natural hydrological pro-cesses (Niemczynowicz 1999) to support water supplyand sanitation, storm-water management, and floodprotection. Water scarcity–too little—can be natural,for instance due to droughts or in desert cities, butcan also be the result of over-use and poor manage-ment (Rijsberman 2005, Padowski et al 2016). Waterscarcity can be addressed with infrastructure, yet dams,canals, desalination plants and other technical solu-tions are not without problems: they usually requireconsiderable funding; municipalities need to collab-orate with regional and national administrations toaccess water resources that are outside their jurisdic-tion; and large-scale infrastructure development canhave significant environmental and social impacts.Water demand management as a way to addressscarcity receives increasing attention, yet changingpeoples’ behaviour to curb wastage and achieve effi-cient allocation of water to its most valuable use isfraughtwithbehavioural, social, economic andpoliticalchallenges (Fielding et al 2013). Flooding—too muchwater—can originate from the sea (coastal floods),rivers (fluvial floods) and rain (pluvial floods). Thesecauses are often linked: heavy rains causing swollenrivers with backflow due to high tides driven by storms.Cities in river deltas are especially vulnerable to flood-ing. Still, people tend to settle in flood prone areasbecause of the fertility of land and accessibility ofwater transport, resulting in complex interactions andfeedbacks between sociological and hydrological pro-cesses (DiBaldassarre et al2013).Waterpollution—toodirty—can contribute to water scarcity and impacthealth of ecosystems and humans (Biswas and Tor-tajada 2011). When groundwater or surface waterresources are contaminated they are not suitable for

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supplying drinking water without treatment, whilepoor citizens may not be able to afford treatmentand are subject to health risks. Infectious and non-infectious waterborne diseases are globally a majorsource of human suffering and economic damage. Poorsanitation can cause urban water pollution, while arange of other point and diffuse sources of urban waterpollution exist as well, including industrial dischargeand surface runoff. In many ways, addressing waterquality issues is much more complex than address-ing water quantity issues (Biswas and Tortajada 2011,Falkenmark 2011).

Urban water systems interact with many other sys-tems and hence are affected in indirect ways, and atthe same time water problems indirectly cause otherissues. In this respect,Zeitoun(2011) introduces a ‘web’of water security that focuses on interdependenciesof physical and social processes and interdependen-cies with other security areas, such as climate security,food security, energy security and human security. Aclear example of complex interactions at the urbanscale is the issue of land subsidence. Over-abstractionof groundwater in many coastal cities, most notablyJakarta (Abidin et al 2011), causes subsidence result-ing in increasing coastal, fluvial and pluvial floodhazards, and water quality is affected through salineintrusion. Lack of good quality surface water, inade-quate investments in and governance of water supply,and poor enforcement of groundwater pumping con-tribute to worsening urban water security. Anotherexample of interdependencies is the phasing out ofa relatively large and viable pig farming industry inthe 1980s in Singapore due to water quality con-cerns (Tortajada et al 2013), while at the same timeindustrial policies have increased the share of non-domestic water consumption to 55% in the city-state(www.pub.gov.sg), showing the strong interaction ofwater, social and economic issues. Interaction of urbanwater systems with other systems also takes place atthe regional, national and global scale through thewater footprint of urban consumers (Paterson et al2015). Consumption of food and other commoditiesin cities affects water use elsewhere, while at the sametime dependence onwater resources elsewhere throughtrade can affect urban water security.

Urban water issues are dynamic. A range of socio-economic, environmental and governance-relateddrivers cause adaptations and transformations in urbanwater systems over time (Daniell et al 2015). Changingpatterns of temperature, evaporation and precipitationas a result of climate change, growing urban popu-lations, changing river flows as a result of upstreamwater and land use changes, technological changes anddevelopment of new preferences and norms are allexamples of drivers for changes in the way water isbeing managed. The dynamics occur across differentscales (Wheater and Gober 2013). Water issues at theurban scale are connected to global climate change,regional basin changes and changes in consumption

preferences of citizens. The dynamics and cross-scaleinterlinked systems give rise to complexity and uncer-tainty challenges that need to be addressed to improveurban water security.

3.3. Goal-oriented perspectivesWater security is often conceived as a good or as agoal to be achieved. The traditional water manage-ment literature speaks about the ‘functions of a watersystem’. In the environmental sciences, a more com-mon term is ‘ecosystem services’ or ‘environmentalservices’, which when applied to water systems trans-lates into ‘water system services’. Typical water-relatedservices to be fulfilled include: urban water supply;sewerage; urban drainage; flood risk protection; navi-gation; provision of recreational and aesthetic values;and provision of ecosystem values. Much of the urbanwater security literature considers various aspects of thedifferent water systems functions. According to Larsenet al (2016), the top priorities for urban water sus-tainability include the provision of safe drinking water,wastewater handling for public health, and protectionagainst flooding. But often ‘water security’ is narroweddown to just ‘water supply security’ (e.g. Lundqvistet al 2003, Padowski et al 2016, Grafton 2017). Animportant driver of the focus on water supply has beenthe UN goal to increase the number of people withadequate water supply and sanitation, as first laid downin the Millennium Development Goals and later inthe Sustainable Development Goals. The goal-orientedperspective raises the question of water security forwhom: for every urban citizen equally, or primarilyfor the richer areas and business districts of the city;and for the water users in the city, or also for thoseusers in the catchments where water is extracted forurban use. The question ‘security for whom’ oftenremains unanswered.

3.4. Integrated-water versus water-integrated per-spectivesWhereas many studies are rooted in the idea of inte-grated water management, acknowledging that oneshould consider all aspects of water in coherence,water is increasingly seen as just one component thatshould be integrated in the broader scope of develop-ment and environmental policy. For instance, watersecurity is increasingly being studied in relation tofood and energy security. Most of those studies donot particularly relate to the urban level, but sev-eral do. Most of the urban water footprint studiesshow that the external water dependency particularlyrelates to food import into the city. Urban food essen-tially depends on the availability of sufficient landand water resources elsewhere to produce the food.In some cases, urban energy security also depends onthe water resources elsewhere, for instance in the caseof urban electricity depending on hydropower. Butalso in the case of electricity through thermoelectricpower plants, water scarcity can affect energy supply,

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Figure 5. Pressure-state-impact-response schematization.

as Sovacool and Sovacool (2009) show for fourmetropolitan areas in the US (Houston, Atlanta, LasVegas, New York). With ongoing replacement of fos-sil fuels by biofuels, urban transport increasingly relieson external land and water resources elsewhere againto grow the biomass required to produce the bio-fuels. Conversely, urban water supply is consumingincreasing amounts of energy (Kenway et al 2011).It has been estimated that the California State WaterProject, delivering water mostly to urban water usersin California, is the largest single user of energy inCalifornia, using 2–3% of all electricity consumed inthe state, which is equivalent to about one-third ofthe total average household electric use in the region(Cohen et al2004).Urbanwatermanagementmeasures(like water conservation or reuse) may actually greatlyimpact on energy use and carbon emissions as Shresthaet al (2012) show in a case study for Las Vegas. Theconcept of ‘integrated water management’ may thus bereplaced by an increasing need to get water concernsintegrated into urban planning and urban energy andfood supply policies.

3.5. Policy analytical versus governance perspectivesWater security is not just about having a good water sys-tem status and about the proper fulfilment of variouswater system functions, but it is also about good gov-ernance (Bakker and Morinville 2013). Urban watersecurity requires both integrated analysis and plan-ning (considering all aspects and functions of the watersystem) and coherent policy making across differentrelevant governmental institutions. Inpractice, though,we observe that scholarly emphasis generally lies onthe one or the other. Whereas engineers and urbanplanners tend to design effective solutions on the draw-ing table, underestimating the processes needed toactually implement those solutions, public adminis-tration and political scientists are inclined to worryabout policy processes, stakeholder interactions, legit-imacy and power, looking for mechanisms of goodgovernance but underestimating the quality and effec-tiveness of policy outcomes. ‘Good’ solutions on thedrawing table are often not feasible (hence one mayquestion whether they are good), but ‘good’ gover-nance does not guarantee outcomes that are effective interms of solving the problems at hand. The final resultdepends on balanced attention to both the bureau-cratic and technocratic aspects of planning and theadministrative, institutional and political aspects of

governance. There is rather good knowledge, for exam-ple, what could be efficient and effective water pricingschemes, but the likelihood that changes in water pric-ing structures are accepted at all may be rather afunction of smart governance, finding the right coali-tions, making combinations with other issues, andbalancing interests.

4. A systems perspective on urban watersecurity

For an understanding of the complexity and timedimension of urban water security, it can be helpfulto adopt a system-dynamic perspective, acknowledgingthat many variables, causal mechanisms and feedbackprocesses play a role. In other fields of environmentalstudy, the pressure-state-impact-response schematiza-tion of social-environmental systems facing changehas been proven helpful in one form or another ina first rough description of what makes systems change(e.g. OECD 1993, EEA 1999, Hoekstra 2000). First ofall, there are the driving mechanisms of change thatexert pressure on the system (figure 5). In the case ofurban areas, major pressures that change the water sys-tem include both environmental pressures (like landuse and cover changes and climatic changes withinthe urban area, and changes external to the urbanarea, like changing water availability in the areas onwhich urban consumption depends and sea level rise)and socio-economic pressures (like continued popu-lation growth, changing water demands). The state ofthe water system can be described in terms of waterstocks and flows within the area, exchanges with itssurrounding areas, occurrence of extreme events suchas droughts and flooding, water quality and availableinfrastructure. Impacts of the water system state onits functions or services can be described in terms ofactual (clean) water supplied and security of (clean)water supply, actual flood protection levels provided,etc. Finally, responses can include institutional reform,new plans, implementation of plans and operation andmaintenance. Effective responses will reduce pressures(e.g. moderate continued urbanization, decrease waterdemand through water pricing or other measures),improve the state of the system (e.g. through improvedinfrastructure) or reduce impacts (e.g. through spatialzoning, disaster planning). In the complex, dynamicsystems that cities are, where social and physical

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processes interact, understanding of feedback loops isimportant, as they can cause lock-ins, such as the leveeeffect described below, and undesirable outcomes ofresponses. Urban water security is equally complex anddynamic: transitions over time affect the water secu-rity of a city and require anticipatory and proactiveresponses.

4.1. PressuresCities face a large number of pressures that affectwater security. The pressures can be grouped in socio-economic and environmental factors. An importantsocio-economic factor is urbanization: ingrowingcitieswater demands increase with population growth andon top of that per capita consumption increases witheconomic development. To meet increasing demands,renewable local water resources may not be suffi-cient, leading to over-exploitation of surface water andgroundwater resources, including the consumption offossil groundwater, or the need to use (additional)external water resources. Most cities already dependon water resources from outside the municipal bound-aries (McDonald et al 2014) and growth means thatincreasingly remote water resources need to be tapped,either from within the same catchment where the citylies or from other catchments, possibly conflictingwith other water uses. The water footprint of grow-ing cities also expands, and cities with large externalwater footprints could face pressures from unsus-tainable production in source regions. With morepeople and assets, exposure to water-related hazardsalso increases. Flooding risks can increase as imper-vious areas expand, and more people generate morewaste affecting water quality. In developing cities exis-tence of slums and families living below the povertyline may add to the pressures as these areas have noproper water and sanitation infrastructure. In addition,some cities can face specific socio-economic pressures,such as the presence of water-intensive industries,widespread open defecation or gender issues in accessto water and sanitation.

Environmental pressures are caused by the hydro-logical and geographical conditions in the area wherea city is located and changes in these conditions. Somecities are located in areas with an unfavourable cli-mate, such as an arid climate, a climate with largeintra or inter-annual variability in precipitation, or inareas prone to hazards such as hurricanes, floods anddroughts. Climate change modifies these conditionsin the long run, changing the water security situationas well. Cities may be located in low-lying areas andthreatened by sea level rise and land subsidence. Landsubsidence is often the result of urbanization whenunsustainable groundwater abstraction takes place tomeet increasing demand, as mentioned before, or bydrainage to make wetlands suitable for urban expan-sion.

Further growth of cities and climate change arelikely to cause larger water stress in cities, both in

terms of flood problems and water scarcity, whilehigher temperatures could also affect water quality.McDonald et al (2011) estimate the amount of waterphysically available near cities and show that currently150 million people live in cities with perennial watershortage, defined as having less than 100 litre per per-sonperdayof sustainable surface andgroundwaterflowwithin their urban extent. They further estimate thatby 2050, demographic growth will increase this figureto almost 1 billion people. Climate change will causewater shortage for an additional 100 million urban-ites. Freshwater ecosystems in river basins with largepopulations of urbanites with insufficient water willlikely experience flow regimes that do not longer meetthe environmental flow requirements to maintain.

4.2. State of the water systemThe state of an urban water system concerns the quan-tity and quality of water, and the infrastructure tomanage these. The quantity of water in a city canbe described in terms of water stocks and flows andexchanges with areas outside the municipal bound-aries. Groundwater extraction from wells within andoutside municipal boundaries is an important sourcefor urban water supply. For instance, a study con-ducted in 1998 found that in northern China half ofthe urban water demand was met by groundwater, witha rapid decline of water levels in most cities since thelate 1970s (Zaisheng 1998). Globally, many aquifers areoverexploited: water withdrawals are exceeding aquiferrecharge leading to depletion of the aquifer (Wadaet al 2010). Surface water is another important sourcefor urban water supply. Many cities are located on riverbanks, yet water abstraction points are often locatedupstream where water quality is better, as in the cityand downstream sewage water is discharged. Reser-voirs can be constructed to create a buffer to managevariability in surface flows. To assess the state of riverflows they can be compared to what they would beunder undisturbed conditions and to environmentalflow standards (e.g. minimum flows to maintain cer-tain ecosystem values). Similarly, surface water andgroundwater quality canbe compared to ambient waterquality standards, for both chemical and biologicalpollutants. Biological contamination is particularly rel-evant for shallow groundwater wells, often used byhouseholds in cities with inadequate water supply sys-tems, which are contaminated from leaking sanitationinfrastructure (leaking sewers, septic tanks, latrines,etc.). Aside from groundwater contamination, pollu-tants can accumulate in surface water sediments overtime. In coastal cities, salt water intrusion can also affectthe state of the water system and make groundwaterwells unusable. Finally, it should also be noted thatthere is a strong link between solid waste managementin a city and garbage in streams and canals.

Water supply infrastructure, sanitation infrastruc-ture and flood protection infrastructure should beconsidered when looking at the state of urban water

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infrastructure. Relevant indicators for the state ofthe infrastructure include coverage of water supplysystems in terms of connection rates and supply capac-ity; drinking water quality standards; percentages ofwastewater collection and treatment, distinguishingbetween primary, secondary and tertiary treatment;leakages in drinking water supply and sewerage sys-tems; and adequacy of stormwater and flood protectioninfrastructure (levees, weirs). The latter should bebenchmarked against projections for sea level rise andclimate change as the investment horizon for this typeof infrastructure is long.

4.3. Impacts on water services and functionsWhile the state of the water system is mostly describedin physical terms, the impacts focus on how wellthe water system provides its water supply and san-itation, flood protection, recreational, environmentaland other services. A wide variety of indicators isused to benchmark water utilities (Berg and Marques2011, www.ib-net.org); in addition to indicators for theperformance of the physical infrastructure, these alsoinclude for instance management and financial perfor-mance indicators. Forwater supply, theultimate impactfollowing pressures and state is how many peoplehave adequate water supply and sanitation services: theinfrastructure may be there, e.g. households may havea connection to the water supply system, but if watersupply does not meet demand, breaks down duringdroughts, or is contaminated, impacts on households’wellbeing may be severe. Similarly, if water can be sup-plied, but it is not affordable for poor households, thewater system is not functioning properly. Occurrenceof waterborne diseases is a measurable impact of inad-equate water supply and sanitation. Similarly, coastal,river and stormwater flood protection infrastructuremaybepresent,butultimatelywhat counts is thatfloodsdo not occur. Frequency, severity and extent of flood-ing are important physical indicators for adequacy offlood protection infrastructure, while annual damagesand casualties focus on the social dimension. Humanuse of water resources in cities has severe impact onthe environmental services: biodiversity decreases ascompared to reference situations or targets, toxics andplastics can end up in aquatic species, algae bloomfrequencies can increase and fish kill incidents canoccur. Finally, water has an aesthetic and recreationalfunction in many cities such as Venice, Amsterdam,Stockholm and Singapore. The degree of cleanlinessof waterways and waterbodies directly impacts thesefunctions (Carson and Mitchell 1993).

Urban water impacts extend beyond the munic-ipal boundaries. As cities depend on external waterresources, conflicts over limited supplies could arise.Rural water uses are usually sacrificed for urban uses,but rural users would need to be adequately compen-sated for any negative impacts, such as loss of income.In addition there is the dependence of the water foot-print of urban consumers on external water resources

for producing the food consumed within the city.For both types of dependence, the impact is not somuch related to the dependence itself, this is inherentto urban areas, but the degree to which the dependencyon external water resources is unsustainable given theavailable water resources in the source regions.

4.4. ResponseResponse aims to decrease pressures, improve thefunctioning of the water system and reduce nega-tive impacts of a malfunctioning water system onwater services and functions (Sekovski et al 2012).Response results from a perceived mismatch betweenan actual and desired situation or from a undesir-able future situation. While the focus is usually ongovernmental response, societal response is equallyimportant. An example of the latter is the installa-tion of household groundwater wells in cities with aninadequate piped water supply system. As urban watersystems are complex and dynamic, responses requireinnovation and development in almost all technical,institutional and organizational dimensions (Larsenet al 2016) with their own timeframes and scopes.In addition, many responses require dealing withuncertainty and ambiguity, e.g. when it concernspolicy-making for future climate change. Conse-quently, a significant body of literature exists on policyor decision-making under uncertainty and creatingresilient, adaptive and robust systems in the (urban)water sector (e.g. Gersonius et al 2016, Johannessenand Wamsler 2017). Larsen et al (2016) discuss fivealternative non-exclusive and partly overlapping solu-tions to conventional urban water management (table1).Althoughtherearemanymore, city andcase-specificresponses, these five responses cover a good part of thechallenges cities globally face.

4.5. Transitions over timeBased on a historical analysis of the changing insti-tutional and technological arrangements supportingAustralia’s urban water management practices over thelast 200 years, Brown et al (2009) propose a frame-work to understand how urban water managementin cities generally transitions when moving towardssustainable urban water conditions. They distinguishbetween six subsequent stages in the ‘urban water man-agement transitions framework’ (figure 6): the watersupply city (with a focus on the effective provision ofsafe and secure water supply), the sewered city (addedfocus on sewerage in response to epidemic outbreakof diseases), the drained city (added focus on urbandrainage in response to the increasing damage fromstormwater), the waterways city (added focus on thecleanliness of water bodies and wastewater treatmentin response to increasing water pollution), the watercycle city (added focus on water demand managementand closing water and substance cycles in response tolimitations to water supply and assimilation of pol-lution), and the water sensitive city (added focus on

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Table 1. Emerging solutions to urban water challenges (after Larsen et al 2016).

Local water storage andstormwater drainage

Concepts such as low impact development, water sensitive urban design and sustainable urban drainagesystems try to address the negative impacts of urbanization on stormwater runoff (Fletcher et al 2015), andin some cases also to sustainably increase the use of urban catchment water as a resource. Green roofs,rainwater harvesting and local water storage may flatten runoff peaks and increase local water supply.

Increasing water productivityand non-conventional watersources

Water recycling and reuse aim to increase water productivity. Several cities in water-stressed areas treatwastewater for use in irrigation or other uses. A few cities, e.g. Singapore and Windhoek, have developed

systems to recycle wastewater for potable use (van Rensburg 2016), although direct potable use still facesemotional and psychological barriers (Leong 2016). Desalination is another technology to increase supply,but it is still more energy-intensive than water recycling.

Waste prevention andseparation of waste at thesource

Reducing the use of potentially harmful chemicals and preventing them from ending up in wastewater canreduce water pollution and the challenge of wastewater treatment significantly. Water recycling can besupported by source separation of wastewater, which makes recovering nutrients and energy easier.

Distributed or on-sitetreatments

With advancing technology, the need for large centralized infrastructure could reduce in favour ofdistributed, on-site systems that can be implemented in the short-term and can be suitable especially forcities that currently have poor infrastructure as they do not require large-scale investments.

Institutional andorganizational reforms

Many undesirable pressures, states and impacts are the result of governance failures at multiple levels ofgovernance (Pahl-Wostl 2017) and require institutional and organizational reforms. Involvement of theprivate sector and decentralization have been proposed as panaceas, yet water policy and management is

complex and new perspectives, concepts and frameworks, such as adaptive and transformative change, sociallearning, self-organizing systems, informal networks and poli-centricity have emerged to understand this.

Figure 6. Urban water management transitions framework (based on Brown et al 2009).

adaptive, multi-functional infrastructure and urbandesign reinforcing water-sensitive behaviours as aresponse to climate change). The transitions are under-pinned by cumulative socio-political drives and in eachstage new service delivery functions are added. Thereare currently no ‘water sensitive cities’ in the world,but according to Brown et al (2009) the concept isattracting increasing attention from scientists and prac-titioners. The transitions framework suggests that eachstage brings urban water management at a higher levelof advancement, and one may argue a higher level of‘water security’. Yet, as acknowledged by Brown et al

(2009), the transitions through different stages is notso linear. Different aspects of urban water systems canbe at different stages concurrently and besides pro-gression, also degradation is possible. These complexdynamics cause water security to change over time,and sometimes not in obvious ways. An example isthe levee effect (Di Baldassarre et al 2013), wherebylevees to protect against floods meant to increasewater security actually increase the vulnerability, andhence reduce water security, as people have no longerexperience to deal with floods and protected areasdevelop faster.

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Table 2. Overview of urban water and sustainability indices.

Urban water indices Urban sustainability indices

City Blueprint van Leeuwen et al (2012),Koop and van Leeuwen

(2015)

Green City Index Siemens (2012)

Sustainable City Water Index Arcadis (2016) City Resilience Index Arup (2014)

Water Provision ResilienceIndex

Milman and Short (2008) SDEWES Index SDEWES Centre (2017)

Sustainability Index forIntegrated Urban WaterManagement

Carden and Armitage (2013) National Water SecurityIndex, including the aspect ofurban water security

ADB (2013, 2016)

Urban Water Security Indicesand Indicators

Jensen and Wu (2018)

5. Urban water security indices

As discussed in this paper, urban water security isa very broad concept that can be approached frommany different perspectives. The concept is often usedqualitatively, yet there is value and interest in quanti-tatively measuring urban water security (van Beek andLincklaen Arriens 2014). Quantification of urban watersecurity makes the concept more concrete and can helpto carry out assessments, prioritise actions and invest-ments, track progress and inform decisions (Dicksonet al 2016). Indicators and indices can be a powerfulcommunication tool to facilitate discussions betweendifferent stakeholders. There is a very large number ofwater (security) indicators and indices (Plummer et al2012, Dickson et al 2016), though only a few focusspecifically on urban water security (table 2).

The City Blueprint (van Leeuwen et al 2012) is adedicated framework for the assessment of the sus-tainability of urban water management. The updatedversion (Koop and van Leeuwen 2015) focuses onindicators that are within control of local water author-ities, and hence it excludes trends and pressures, suchas climatological variables, water imports and exports(dependent on socio-economic processes), and surfacewater quality (assumed to be caused by upstream pol-lution; wastewater treatment is used as an indicator forsurface water quality). Hence, the index can be consid-ered rather as an assessment of integrated urban waterresources management performance than a compre-hensivewater security index.Data for theCityBlueprintis collected from public sources and assessments byexperts and local water authorities. In general, theframework heavily relies on the data that is available forEuropean cities and for several indicators country-leveldata is used rather than city-level data. The Sustain-able City Water Index was developed as ‘a tool tohelp inform future improvement and long-term watersustainability’ (Arcadis 2016). It is a normalised indexranking cities relative to each other. The index dis-tinguishes three main categories: resiliency, efficiencyand quality, with data obtained from global datasetsof variable spatial levels and municipal water utilities.

The European cities score high, with a top-5 consistingof Rotterdam, Copenhagen, Amsterdam, Berlin andBrussels. This may be due to a focus on responses; forinstance, Rotterdam still receives an average score forflooding even though it is a coastal city below sea levelbecause good flood protection measures are in place.Urban water security also has a time dimension. Mil-manandShort (2008) argue that this dimension is oftenoverlooked by existing sustainability indicators. Theypropose a Water Provision Resilience Index that incor-porates the notion of resilience to reflect changes in thestate of the water system over time. The index measureshow well an urban water provider is able to maintain orimprove the percentage of the population with accessto safe water into the future. A qualitative question-naire is used to assess performance in six critical aspectsof urban water supply systems: supply, infrastructure,service provision, finances, water quality and gover-nance. The Sustainability Index for Integrated UrbanWater Management (Carden and Armitage 2013) isa composite index comprising four categories (social,economic, environmental and institutional), whichare represented by a total of 16 indicators that arecalculated using a total of 35 variables. Using stan-dardisation and means a score for each category isdetermined. The index was applied to ten cities inSouth Africa. Jensen and Wu (2018) develop a newurban water security index based on indicators in fourcategories: water resource availability, access to water,water-related risks, and institutional capacity to man-age water resources. They apply this framework to twopilot cities.

In addition to these urban water security indicatorsthere are urban sustainability and resilience indica-tors that include water issues, such as the Green CityIndex (Siemens 2012) which includes one category ofwater indicators, the City Resilience Index (Arup 2014)with 52 indicators of which several link to water, andthe SDEWES Index (SDEWES Centre 2017), whichincludes a category for water and environmental qual-ity. Furthermore, there are several composite watersecurity indicesdeveloped forbasinor country compar-isons (e.g. Lautze and Manthrithilake 2012, ADB 2013,

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Animesh et al 2016, Vorosmarty et al 2010, Gassertet al 2014). The National Water Security Index fromADB (2013, 2016) includes five aspects, of which one isurban water security. Urban water security is measuredthrough indicators of water supply, wastewater treat-ment, and drainage (flood damage), with factors addedfor urbanisation rate and river health. ADB (2016) sug-gests a correlation between national water security andGDP and between national water security and qualityof governance as well.

Although integrated, comprehensive indices ofwater security can be useful for many purposes, theysuffer from conceptual and methodological issues(Garrick and Hall 2014, Molle and Mollinga 2003).Water systems are complex with many interacting partsand causality is often not clear. All indices discussedabove have issues with data availability, requiring theresearch to make assumptions, use expert opinion oruse proxy data, e.g. country level data for cities, eventhough geographical variation may be large. Data qual-ity may also be an issue and needs to be discussed clearlyto avoid wrong interpretations. Composite indices usu-ally classify indicators into several categories or tiers,with results displayed at a higher tier. Constructingindices and indicators that combine several dimen-sions requires subjectively assigning weights (includingequal weights) and results in information loss. A dash-board approach, in which all individual variables aredisplayed, may partly remedy this.

6. Conclusion

In its most comprehensive interpretation, the con-cept of urban water security addresses the fulfilmentof all different ‘water system services’, considers over-all welfare as well as social equity and environmentalsustainability, and addresses both risks and uncertain-ties. Risks include hazards, exposure and vulnerability,the latter including aspects of coping capability andresilience. In this all-encompassing approach, urbanwater security may be seen more or less as equal to whatothers would call ‘urban water sustainability’ (wheninterpreted in its broadest sense as well). Therefore, itcan happen that what the one calls a ‘sustainable citieswater index’ may actually aim to capture the same aswhat others would call an urban water security index.A systems approach can be helpful to comprehend thecomplexity of the urban system, including its relationwith its (global) environment, and better understandthe dynamics of urban water security.

Future research may focus on the question howto transition towards cities that are more inherentlyhealthy, sustainable and resilient. Most cities in theworld are still struggling to solve problems created(water shortages, water pollution, flood vulnerabil-ity), using end-of-pipe solutions (larger pipes carryingin water from further away, wastewater treatment,dikes). We need to better understand the full potential

of water sensitive design, rainwater harvesting, recy-cling, reuse, pollution prevention and other innovativeurban water approaches. We need to consider‘integrated water’ approaches, where all water issues areconsidered comprehensively and in their mutual inter-dependencies, as well as ‘water integrated’ approaches,whereby handling water wisely forms an integral partof urban dynamics and urban design. Understandingand finding suitable governance arrangements in localcontexts supporting these approaches is a clear researchneed as well. In addition, a proper understanding of thefundamental dependence of urban areas on their localhinterland for water supply and the global hinterlandfor supply of food and other water-intensive goods, willbe needed to understand the true water security of citiesin the long run.

ORCID iDs

ArjenY Hoekstra https://orcid.org/0000-0002-4769-5239

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