The only thing I know for certain that ACV does .. is help prevent algae growth in water. There's been lots of discussion on health benefits, reducing pasty butt, etc. That being said, I put 1 tablespoon per gallon of water in all of my waterers. I've never had an issue with it - tho I change out the water in them at minimum every other day when it's really hot. In cooler temps, I've had a 5 gallon waterer last 4-5 days and no issues.
For some perspective, I have 1 run, 1 pen, and 1 mini-coop/pen. Each run and pen has 2 5 gallon bucket nipple waterers, the mini-coop/pen has 1 of them, and I have another inside the main coop. I have 6 5 gallon watering stations for 23 chooks.