"How do you calculate how much water is needed for a given area?"

I received this inquiry by email:

When looking at water quantity for a new golf course, you have to determine how much water is needed obviously so what I want to know is

1. How do you calculate how much water is needed for a given area (the whole golf course?)

2. I know you have to look at the driest year data and base it on that but I understand you have to measure how much a grass plant and soil will lose via Evapotranspiration so you know what you have to replace so what methods do you use to find this out?

I suggest calculating a water budget for the location using the method described by Gelernter et al. with this supplement providing the details for the calculations.