Water use by livestock: A global perspective for a regional issue?

Abstract

Water scarcity, a function of supply and demand, is a regional issue with global repercussions, given that 1) the increasing human population and demand for animal products will increase water demand and influence international trade in agricultural products and that 2) global climate change is altering rainfall patterns worldwide. Water can be divided into the following types: blue (i.e., surface and groundwater), green (i.e., soil water used in evapotranspiration), and gray (i.e., water necessary to dilute pollutants). On a global scale, agriculture represents 70% of blue water use. One main difference among all methods for assessing water use is whether and how they include green and gray water. The “water footprint” approach includes green water, whereas life cycle assessment approaches tend to exclude green water or to include only the variation in green water resulting from changes in land use. A second difference is whether water use is reported as a volume of water or as an index of water-use impact (e.g., H2O equivalents). A third is whether water that returns to the same location (e.g., in urine) is considered to have been consumed. Because of these differences and the fact that existing studies have analyzed only a limited number of different livestock production systems, methods give wildly different results for the same livestock product. For example, estimations of water use to produce 1 kg of beef range from 3 to 540 L of H2O or H2O equivalents for the life cycle assessment approach and from 10,000 to 200,000 L of H2O for the water footprint. Ultimately, water scarcity depends on blue water use. Decreasing the contribution of livestock to water scarcity can be achieved by decreasing feed irrigation. Livestock farming also has positive impacts on the environment related to water use.