Union of Concerned Scientists gives an overview of how water is used in the generation of electricity. I came across this Op-Ed at the NYT that claimed more water is used for electricity than agriculture, and just could not believe it, but apparently if you look at surface water withdrawals, it’s true (power: 41%, ag: 37%). “Withdrawal” just means the water is taken from the river/lake/whatever. Usually most of it is put back (hotter), which means it can be used again for agriculture. In any case, the Texas grid came very close to shutting down 10% of its generation in 2011 because of the drought, right as it was experiencing its highest ever loads. Yet another fun climate-energy feedback.