Some quick googling suggests there are 4 cups of almonds in a gallon of almond milk, and ~25 almonds per cup, so about 100 gallons of water per gallon of almond milk from just growing the almonds. That's a factor of 20x, if we believe it takes 2000 gallons of water to make a gallon of milk.

But another source on the top links of Google says it takes about 4 gallons of water to make a gallon of milk. This is a difference of 250x. That would imply almond milk takes 25 times as much.

It shocks me how such a seemingly basic consumer question could have such wild orders of magnitude variance in the apparent answers.