I thought almonds use 10% of CA's water budget. That's for just almonds by themselves and almonds in milk. Something like 70%+ of those almonds get shipped to China and there's still enough to fill every store in the world with cream cheese, regular cheese, butter, milk, and dry form. 80% of all Almonds on earth come from California.

Animal agriculture accounts for 47% of California's water use, though it's hard to say exactly what comes from where.

To try to figure out how much is used for just cow's milk we know that 41.2 billion pounds was produced in 2008 each gallon of milk is 8.6lbs.

That's 4.79 billion gallons of milk. Using the numbers from your study cow's milk is 291.47 gallons/gallon. The dairy industry puts the number at 144, so we'll use both to establish a range.

That's 676.8-1370 billion gallons of water to make the milk in California in 2008. I couldn't find 2008, but for 2010 California used 42,600,000 acre-feet of water. So that's 13.9 trillion gallons of water. in that year.

That's 4.87-9.85% of California's water use, just for cow's milk. Cow's milk, not all beef. Not all animals. Just cow's milk. Cow's milk is 50-100% the water use of almonds in California.

To compare efficiency rather than just numbers California produced 1.46 billion pounds of almonds in 2008

Almonds are 2608 kcal/lb. Cow's milk is 277 kcal/lb.

1.462608 = 3807 billion calories for that year's almond production. 4.79277 = 1327 billion calories for that year's milk production.

So assuming the high end number you get 2.87 * more calories per gallon of water in almonds (not almond milk specifically, all almonds) than you do in cow's milk. The low end estimate would be x1.43.

So there you go, there's some more numbers. I really think that every food stuff should be broken down to per nutritional unit water usage, not per volume/weight water usage. Same too with CO2e. Without that comparison it's impossible to really understand what is more or less efficient.