Book excerpt: The Technical Advisory Group (TAG) for Water Use Assessment, composed by 30 international experts, has developed guidelines on water footprinting for livestock supply chains. The mandate of the Water TAG was to provide recommendations to monitor the environmental performance of feed and livestock supply chains over time so that progress towards improvement targets can be measured; apply the guidelines for feed and water demand of small ruminants, poultry, large ruminants and pig supply chains; build on and go beyond the existing FAO LEAP guidelines; and pursue alignment with relevant International Organization for Standardization (ISO) standards, specifically ISO 14040, ISO 14044 (ISO, 2006b and 2006a) and ISO 14046 (ISO, 2014). The guidelines on water use assessment include the impact assessment: the assessment of the environmental performance related to water use of a livestock-related system by assessing potential environmental impacts of blue water consumption following the water scarcity footprint according to the framework provided by ISO 14046 (ISO, 2014); and the assessment of the system’s productivity of green and blue water. The guidelines are thus intended to support the optimization of use of water resources and the identification of opportunities to decrease the potential impacts of water use in livestock production. The Water TAG guidance is relevant for livestock production systems, including feed production from croplands and grasslands, and production and processing of livestock products (cradle-to-gate). It addresses all livestock production systems and livestock species considered in existing LEAP animal guidelines: poultry, pig, small ruminant and large ruminant supply chains.