Animal products vary in the amounts of water required for their production, but they all require far more water than vegetables.i For example, producing 1 kg (2.2 lbs) of potatoes or corn requires 600 L (158 gal), or 70 gal of water per pound. In contrast, producing 1 kg (2.2 lbs) chicken requires 3,500 L (924 gal), or 420 gal of water per pound - 6 times the amount of water it takes for potatoes.
Growing 1 kg (2.2 lbs) of pig requires 6,000 L (1,585 gal), or 720 gal of water per pound - 10 times the water for 1 kg of corn. Raising 1 kg (2.2 lbs) of cattle requires 43,000 L (11,359 gal), or 5,163 gal of water per pound - 72 times the water it takes to grow vegetables. And, 1kg (2.2 lbs) of sheep requires approximately 51,000 L (13,472 gal), or 6,123 gal of water per pound -85 times the water for potatoes.ii
It requires 5,163 gallons of water to produce one pound of cattle carcass. To put that into perspective, an average U.S. swimming pool contains 22,500 gallons of water. A swimming pool’s worth of water would produce only 4.3 pounds of cow carcass.
A 1,000 pound cow typically yields around 610 pounds of cow flesh. So, a swimming pool’s worth of water water is required to produce less than 1% of the animal that is turned into edible carcass. Or, to produce all 610 pounds of cow flesh, 140 swimming pools worth of water or over 3 million gallons, is needed. According to the American Meat Institute, in 2012 America produced 26 billion pounds of cow carcass. So it took 134 trillion gallons (507 km3) of water to produce cow carcass in 2012.
Comparisons between vegetarian and non-vegetarian diets have illustrated vast differences in their water use and environmental impact. Both healthy and vegetarian diets result in substantial water footprint reductions, and the largest reduction is with a vegetarian diet.iii Studies that compare vegan diets to vegetarian and non-vegetarian diets, are examined later.
Animal-based foods generate more GHGs than plant-based foods, with the exception of fruit and vegetables grown in greenhouses. One study shows that the water footprint (WF) of any animal product is larger than the WF of a crop alternative with equivalent nutritional value.
For example, the average WF per calorie for cow carcass (10 L kcal) is 20 times larger than for cereals and starchy roots (0.5 L kcal). The WF per gram of protein for milk, eggs and chicken (around 30 L g protein) is 1.5 times larger than for pulses (20 L g protein).iv
Meat’s resource intensity depends on two crucial factors. The first is due to the sector's immense scale, at 70 billion land animals. The second has to do with an animal's efficiency to turn its food into body mass known as feed conversion ratios (FCR), that is, units of feed compared to edible carcass.
The range of FCRs is based on the type of animal, and the ratios are approximately 7:1 for cow carcass, 5:1 for pig flesh, and 2.5:1 for chicken. The larger the animal, the larger the percentage of that animal’s body mass is inedible material like bone, skin and tissue. This is why cow carcass conversion ratios are the highest.
In general, cows raised for carcass have a larger total WF than pigs, which in turn has a larger WF than chicken, but the average global blue and gray WFs are similar across the three carcass products. Taking into consideration grazing systems, the blue and gray water footprints of chicken and pig flesh are greater than those for cow carcass.v
The same is true when we look at the water footprint per calorie or protein. The average water footprint per calorie for cow carcass is twenty times larger than for cereals and starchy roots.
i D. Vanham. 2013. "The water footprint of Austria for different diets," Water Science and Technology, 67. 4.
ii David Pimentel, Bonnie Berger, David Filiberto, Michelle Newton, Benjamin Wolfe, Elizabeth Karabinakis, Steven Clark, Elaine Poon, Elizabeth Abbett and Sudha Nandagopal. 2004. "Water Resources: Agricultural and Environmental Issues." Oxford Journals Science & Mathematics BioScience Volume 54, Issue 10Pp. 909-918.
iii D. Vanhama, A.Y. Hoekstrab, and G. Bidoglioa. 2013. "Potential water saving through changes in European diets," Environment International, Volume 61, November 2013, Pages 45–56.
iv Mekonnen and Hoekstra 2012