If we've posited a desert based system, I'm going to guess it is closed loop with respect to water (which is to say the water never leaves the system as anything except perhaps evaporation during post processing.) So the initial water budget probably comes from the aquifer or is imported. Once the system is running an interesting question is how much water would it lose over time.

And while that is an interesting question, it doesn't change the situation that no farmland was harmed in the process. :-)