I was watching 4 chickens for a friend not too long ago, and she asked me to change the water every other day (2 gallon waterer). In two days they were down to the dregs (but not out). BUT--and this is important--that'll change depending on the temperature and other things.
actually chickens are like humans they drink more water if it is fresh so I never felt that 4 chickens would need a 5 gallon waterr I always cleaned and changed my waterers twice daily and had gallon waterers the more the chicken drinks fresh watr the better the taste of eggs water retains the stench of dirty waterers I alwys wanted clean tasting eggs same goes for animals the fresher the water the better health they all have any questions email me
well I change their water like 4 times a day right now LOL! I figured that in the winter it would be harder to change all the time with the loads of snow that we get!!