②AGUPUBLICATIONSWater Resources ResearchRESEARCH ARTICLEHigh-Resolution Water Footprints of Production10.1002/2017WR021923of the United StatesKey Points:Landon Marston1.2 Yufei Ao1.2,Megan Konar1 D,Mesfin M.Mekonnen3 andproduction of any country to dateDepartment of Civil and Environmental Engineering,University of llinois at Urbana-Champaign,Urbana,IL,USA,water footprints of productionDepartment of Civil Engineering,Kansas State University,Manhattan,KS,USA,Robert B.Daugherty Water for Foodbetween locations and economicGlobal Institute,University of Nebraska,Lincoln,NE,USA,"Twente Water Centre,University of Twente,Enschede,thesectorsNetherlands,Institute of Water Policy,Lee Kuan Yew School of Public Policy,National University of Singapore,SingaporeSourding from water-efficientsuppliers (indirect use)reduces waterfootprints more than changes todirect useAbstract The United States is the largest producer of goods and services in the world.Rainfall,surfacewater supplies,and groundwater aquifers represent a fundamental input to economic production.Despitethe importance of water resources to economic activity,we do not have consistent information on waterSupporting Information:.Supporting Information S1use for specific locations and economic sectors.A national,spatially detailed database of water use by sec-.Figure $1tor would provide insight into U.S.utilization and dependence on water resources for economic production.Figure $3To this end,we calculate the water footprint of over 500 food,energy,mining,services,and manufacturingindustries and goods produced in the United States.To do this,we employ a data intensive approach thatintegrates water footprint and input-output techniques into a novel methodological framework.ThisCorrespondence to:approach enables us to present the most detailed and comprehensive water footprint analysis of any coun-try to date.This study broadly contributes to our understanding of water in the U.S.economy,enables sup-ply chain managers to assess direct and indirect water dependencies,and provides opportunities to reducewater use through benchmarking.In fact,we find that 94%of U.S.industries could reduce their total waterCitation:Marston,L Ao,Y.Konar,M.footprint more by sourcing from more water-efficient suppliers in their supply chain than they could by conMekonnen,MM,Hoekstra,A.Y.verting their own operations to be more water-efficient.(2018).High-resolution waterfootprints of production of the United2288-2316.https/doLorg/10.1002/2017W0219231.IntroductionThe United States is the largest producer of goods and services in the world (The World Bank,2017).ThisAccepted 26 JAN 2018economic activity relies on freshwater as a fundamental input to economic production(Rushforth Ruddell,Published online 26 MAR 20182016;Wang et al.,2017).Despite the importance of water to the U.S.economy,it is often undervalued,inef-ficiently utilized,and overexploited(Marston Cai,2016).The first step toward sustainable water allocation(Hoekstra,2014;Hoekstra et al.,2015)is to evaluate how it is currently being used(Chini Stillwell,2017).To obtain a meaningful understanding of how water resources are being used throughout the U.S.econ-omy,detailed spatial and sectoral information are required (Blackhurst et al.,2010).To this end,we calculatethe water footprint of production (Hoekstra Mekonnen,2012)for over 500 unique industries and goodswithin the United States at an unparalleled spatial resolution.Water resources within the United States are projected to be increasingly stressed in the coming decades(Devineni et al,2015).Growing and shifting populations,economic growth,expansion of the energy sector,and warming temperatures,shifting rainfall patterns,and shrinking snowpack due to climate change willalter water supplies and demands (Devineni et al.,2015).These issues are particularly concerning in theAmerican Southwest,which is already water stressed and expected to face greater water scarcity in thecoming decades (Schewe et al.,2014).Furthermore,increasing water allocations to meet environmentalrequirements could further strain existing water uses (Marston Cai,2016).It is essential to understandhow water resources are currently being used in order to better evaluate how future water availability anddemand will impact economic production activities.Water use in the United States is heterogeneous,decentralized,and often politically contentious.This makes2018.American Geophysical Union.it challenging to meter water withdrawals and measure water consumption in a consistent way nationwide.All Rights Reserved.Additionally,there are privacy concerns that prohibit government agencies from reporting some water2288GU Water Resources Research10.1002/2017WR021923uses.For this reason,there is a dearth of national,metered water use information for specific industries andlocations(Chini Stillwell,2017).The USGS runs the National Water Use Information Program,which is acounty-level inventory of water withdrawal estimates.This inventory has provided county-level water with-drawal information every 5 years since 1985(Maupin et al,2014).The USGS employs a variety of methodsto estimate water use of an industry,including surveys,water meters,billing data,remote sensing,models,and water use coefficients.Water use coefficients-one of the most widely used methods for estimatingwater-use-allow for the estimation of water use based off a known variable (e.g.,number of employeesamount of energy produced,area of cropland,etc.).However,the few water use coefficients that are pub-lished are often for a very narrow geographic area and industry,or they are too broadly defined at thenational and sector level.This makes comparison of water use infeasible across different areas andindustries.The USGS water-use inventory primarily presents estimates of the use of water for relatively aggregated sec-tors of the economy (i.e.industry,mining,irrigated agriculture,livestock,aquaculture,and thermoelectricpower)(Maupin et al.,2014).Grouping water-use estimates into coarse sectoral classifications masks impor-tant,yet poorly documented,water-use estimates at more refined industry levels.Another shortcoming of the USGS database is that it does not estimate the contribution of rainfall in meet-ing national crop water requirements.Rainfall is the dominant water supply to crops (Mekonnen Hoekstra,2011a),although irrigation supplies from both surface and ground water sources are also important,espewater,"while water supplies from surface and groundwater sources are called "blue water"(FalkenmarkRockstrom,2004;Rost et al.,2008).Blue water is provided to agricultural water users via infrastructure,suchas irrigation canals,center pivot spray systems,or groundwater pumps.Nonagricultural industries obtainsurface and groundwater supplies through public and private piped infrastructure systems.Since nonagri-cultural industries only consume blue water,water-use estimates of these industries do not incude greenwater.Here,we define water use to be the consumptive use of water resources,following the approach of thewater footprint literature (Hoekstra Mekonnen,2012).Traditionally,water footprint assessments havefocused on agriculture,as it is responsible for 70%of withdrawals globally and is by far the largest con-sumptive user(Gleick Palaniappan,2010;Postel et al.,1996;Vorosmarty,2000).We maintain the waterfootprint framework focus on consumptive water use in order to best capture the role of agriculture (Hoek-stra Mekonnen,2012).Additionally,quantifying consumptive water use will provide a more accurateassessment of the amount of water required for production and enable us to better determine locations ofwater scarcity.This is because water withdrawals ignore the fact that return flows can be utilized manytimes.For instance,water withdrawals in the Colorado River Basin exceed renewable annual supply due tosubstantial reuse of return flows(Richter,2014).There is a growing body of literature that recognizes the important relationship between water resourcesand nonagricultural sectors of the economy,especially in urban areas (Paterson et al,2015).This follows abroader trend of moving to finer spatial resolutions (Mayer et al,2016;Rushforth Ruddell,2015,2016)and industry-specific estimates of water use (Blackhurst et al.,2010;Wang Zimmerman,2016),includingdistinguishing between groundwater and surface water sources(Schyns et al,2015).Yet,no national orglobal study to date combines the spatial resolution,sectoral specification,and water source delineationneeded to provide a meaningful understanding of water use across the ful economy.Subnational estimatesof water use by water source for specific industries would be useful in environmental impact assessments,as noted by Blackhurst et al.(2010),and also enable more efficient water use by setting a localized water-use benchmark.The purpose of this paper is to understand how water is used in specific U.S.industries and locations to pro-duce the goods and services demanded by society.With this goal in mind,we calculate subnational directwater footprints of production (WFP;m/yr)for over 500 goods and services produced within the UnitedStates from 2010 to 2012.Here,direct WFP is defined as the volume of freshwater consumed during thepresent stage of production (i.e.,the water incorporated into a product and/or evaporated during the pro-duction stage of analysis,which does not include cumulative water indirectly used through the supplychain).We also calculate the corresponding water footprint per unit of production(WFU).Presented results2289