My outside waterers are actually the trays off of feeders, leftover from the commercial broiler houses. They work great for outside waterers because they are about 18" in diameter and maybe 3" deep. I refill them several times daily from our well that is 350 ft. deep, so the water is always cold no matter how hot it gets. Since our recent heatwave I've noticed that as soon as I refill them my chickens run over and stand in them. They are cooling their bodies by cooling the blood running thru their feet. This gave me an idea. I dug out the old kiddie wading pool that we used as their brooder and filled it with about 4" of water. Now my chickens stand in it when they need to cool down instead of in the waterers. No more dirty waterers.