Assessment of water use by livestock

Abstract

Water scarcity, a function of supply and demand, is a regional issue with global repercussions, given that i) the increasing human population and demand for animal products will increase water demand and that ii) global climate change is altering rainfall patterns worldwide. Water can be divided into “blue” (surface and groundwater), “green” (soil water subject to evapotranspiration) and “grey” water (water necessary to dilute pollutants to acceptable levels). 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 grey water with blue water. The “water footprint” approach includes green and grey water, whereas life cycle assessment approaches tend to exclude them or to include only the variation in green water availability resulting from land use change. A second difference is whether water use is reported as a volume of water (L) or a volume weighted by a water stress index (L water equivalents). Because of these differences and the few livestock systems studied, methods give wildly different results for the same livestock product. Ultimately, water scarcity depends on blue water use. The contribution of livestock to water scarcity can be reduced by decreasing their water consumption and/or that of the irrigated crops they consume.