First off, if your fogger is making an audible problem noise, letting a middle school use it for a week is probably not the best of ideas.
"Distilled" water is fine because it does not have the chemicals tap water/bottled water does. Try to stay away from CLR. I used it once, months ago, and you can still smell/taste it a bit, it's awful.
I have heard here that vinigar water works great too. 6 parts water, 1 part vinigar.
Good Luck with it!
Chris