Honestly I am reading these and thinking a lot of fresh water gets wasted daily, what's the point of a huge waterer if you are just going to dump it twice a day? It takes years for nature to purify water and a whole lot of energy for man to mass purify it. Keeping their water fresh is great, but if you are going to change it every 8 hours then why use so much? I mean if your 100 strong flock is sucking it up like walking winged fish then cool but otherwise I don't understand.
I don't change it. Don't panic though, I have one of those galvanized 2.5 gallon waters and I use a simple rule, if I wouldn't consider drinking it(mostly meaning its not clear) then I take it over to the hose and use the high pressure setting to flush out any non water particulates. I also add a Tablespoon of Apple Cider Vinegar 'with mother' per gallon, this prevents algae and other nasties from growing, and helps them absorb nutrients, or so I am told, seems to work though.
I also keep it up on some bricks, its probably 5" off the ground, helps alot with keeping it clean.
I've got 3 Hens(RIR, RSL, and ISA Brown).
I can see attempting to cool it down for them, but why not just rotate out some soda bottles, you know, keep one in the freezer while the other thaws in the waterer? I don't like super cold water on very hot days though, the sudden internal temp change hurts some, cool water or tea is great but not cold, cold feels like a brain freeze for my chest, no thanks.