As for cows & global warming (), the link between meat and water use is usually misrepresented. The thread below tries to demonstrate how the commonly cited number of 15,000 (!) liters of water per kg of beef is a very misleading one. 
The water footprint of animal production is said to represent 29% of total agricultural production (and is needed for feed production, grazing, and direct use)
Beef is usually getting the blame, whereby it is said that 15,500 litres of water are needed to produce 1 kg, thus representing 1/3 of the total water footprint of animal production.
However, what this approach overlooks is that most of the water is green water, originating from precipitation (which would fall anyway) and (re)subjected to evapotranspiration.
Green water represents no less than 87% of the water used by livestock, and in the case of grazing beef this number even equals 94%.
Each livestock management system obviously has its own characteristic input of green water, although the latter is the most important category for all systems.
As a result of heterogeneity in production systems, water footprints can be different when comparing different countries (e.g., Italy compared to the world average). carnisostenibili.it/wp-content/upl…
Grass, sustained by green water only, corresponds with 38% of the total water footprint of animal production.
When accounting for green water, LCA estimates for beef raised on predominantly pasture-based systems are 2-221 L/kg LW (~5-500 L/kg beef), which compares to cereal!
Similar numbers were found in another study (18-540 L/kg HSCW), whereby corrections for green water and feed source were introduced.
Likewise, lamb meat production does not necessarily impose a heavy burden on freshwater resource availability, being of the order of only 44 L/kg for lamb cuts.
While variability exists and should not be neglected, it can be concluded that the actual requirements per kg of meat are far below what is usually reported.
