The Water Scarcity Footprint of the US Diet

Abstract

Abstract Objectives Agriculture accounts for 80% of global freshwater consumption, so addressing the water demands of current diets is crucial. Unlike carbon footprints, the impacts of water use are local and dependent on relative water scarcity. New metrics have been developed to assess the amount of water used to produce a product, conditional on its scarcity at the source of production. But little is known about the implications for water scarcity of individual diet choices in the US. Here, we apply this water scarcity metric to individual US diets and assess key contributors to the footprint. Methods Our analysis was based on a global database of watershed-level, geo-spatially explicit irrigation water demand for 160 crops. We used the Available Water Remaining (AWARE) method, applied at the same geo-spatial resolution to establish local water scarcity footprints (WSF) of each crop. These WSFs were aggregated to the national level and adjusted for commodity imports using WSFs from source countries. WSFs of animal-based foods relied on generic U.S. feed rations. Crops were assigned to foods in the Food Commodities Intake Database (FCID), and recipes from FCID enabled linkage to as-consumed foods in the 1-day dietary recall data from individuals (N = 16,800) in the 2005–2010 National Health and Nutrition Examination Survey. Results Animal protein foods account for 33% of the WSF of the average US diet, whereas vegetable protein foods account for 12%, most of that coming from nuts (11%). The contribution of beef (14%) was about 3 times that of chicken (5%). Within vegetable protein foods, almonds (5%), walnuts (3%), and cashews (2%) contributed much more to the WSF than dry beans (1%). Fruit (16%), dairy (9%), and vegetables (9%) were also large contributors to the average WSF. Diets ranked in the top quintile of WSFs account for 43% of the overall footprint, 5.4 times that from the lowest quintile. Conclusions Progress toward sustainable diets should consider the impact of dietary choices on scarcity-characterized water footprints. Major contributors to the WSF of the US diet include meat, fruit, nuts, dairy, and vegetables. Substantial variation of the WSF intensity of individual commodities within these food groups suggests that dietary changes could be made to reduce the impact of agriculture on the use of scarce water. Funding Sources Wellcome Trust #106,854/Z/15/Z.