I've come up with a free method of keeping my chicken's water cold in the summer. I cut the top off 2 liter plastic pop bottles at the point where the sides are straight. I fill these 1/2 to 3/4 (depending if you have a smaller or larger standard waterer) full of water and freeze them. You have to use the straight-sided bottles, not the hour-glass shaped ones. Once frozen, I just run some hot water over them until the giant "ice cube" slides out. Then I put this cube into the chicken waterer. It keeps the water cold for most of the day, depending on how hot it is. The ice cube floats inside the waterer, so it doesn't block the outlet. I would think it also keeps algae from growing as fast, too, as the water is cool. The chickens seem to really appreciate the cold water!