I have a 5 gallon waterer and 19 chickens. I fill it and when it gets down 1/4 full I dump it, rinse it out and refill. I scrub it out when I have the chance but it's not every time. Depending on the weather I have to do it less or more. I have my waterer sitting up so they can't kick anything in it so it stays pretty clean. If I'm going in the morning and I know it's going to be a hot day I'll change the water if it's less than half full. I'm thinking about getting a second waterer for the run.