The “Water footprint” is a popular concept… 

This figure was first released in 2002, when the concept of “water footprint” was established, following the growing popularity of the ecological footprint indicators. Arjen Hoekstra, whilst working at the UNESCO-IHE Institute for Water Education, created the water footprint as a metric to measure the amount of water consumed and polluted to produce goods and services along their full supply chain. Interest in the water footprint grew rapidly after its introduction in academic literature. Today, the Water Footprint Network is working on the harmonisation and promotion of the “water footprint” concept.

…which hides a complex assessment  

The water footprint is an indicator of freshwater use that looks not only at direct water use of a consumer or producer, but also at the indirect water use. It includes actually “three types of water sources”: the blue water (surface or groundwater sourced water consumption by the animals and the irrigation), the grey water (water used to depollute the effluents and recycle them) and the green water (rainfall). 

Livestock’s water footprint is made of 93% “green water”

It is essential to look at the structure of the water footprint. When considering livestock average water consumption, more than 90% is green water (rainfall) captured in the soil and evaporated by the plants and which returns to the water cycle. This would happen with or without farm animals. 

Green water which is part of these cycles, does not reflect the net consumption of water for animal production. Real water shortage may only be based on the blue water. If green water is taken out of the calculation, the scientific community considers that 550-700L are needed to produce 1 kg of beef (including grey and blue water). According to the French national research agency, INRA, 1kg of beef would actually remove around 50L of ‘real’ water (blue water) from the cycle.

Using the same approach, one can estimate that pork meat would require 450L, Chicken meat 300L, eggs 244L and milk 86L as indicated in the table.   

To quote the conclusion of the academic publication Animal Frontiers – “Water is a precious resource that must be conserved globally by all sectors of the economy, including agriculture and thus livestock farming. Tools such as the water footprint and LCA are available, but their interpretation by policy makers has to be refined.“ – conservation of water is necessary, but refinement of the data is required for true measurement of consumption.

Sources:
– https://www.theguardian.com/news/datablog/2013/jan/10/how-much-water-food-production-waste
– M.M Mekonnen et A.Y. Hoekstra, The green, blue and grey water footprint of farm animals and animal products, Value of Water Research Report Series no 48, UNESCO-IHE
https://waterfootprint.org/en/about-us/aims-history
Water footprint assessment manual
http://www.inra.fr/Chercheurs-etudiants/Systemes-agricoles/Tous-les-dossiers/Fausse-viande-ou-vrai-elevage/Quelques-idees-fausses-sur-la-viande-et-l-elevage/(key)/0 
https://academic.oup.com/af/article/2/2/9/4638620