Water usage is great way to divert the populace from what is actually going on
Water isn’t used in the sense it’s “used up”, and converted to another molecule, It’s simply a a conduit of heat energy.
At worst, it’s a cooling tower setup and you can worry evaporative loss, and/or about Legionnaires' disease. Normally it’s simply the same water being returned, but with a slightly higher temperature.
You should be more worried about the computers, and the people running them, than water being heated.