We use a heated dog dish. You can find them fairly cheap.. Here they sell them at walmart and the farm stores. We had 3 of those metal bases last winter, that you set the metal chicken waterer on , and all three of them broke, so we dont use them anymore. Also, instead of just getting water from the hydrant and carrying it in 5 gallon pails, and spilling it all over, thus creating ice. We use old OJ and milk jugs to carry water to the coops to refilll the waterers.
I've been using the big heated dog water bowl from TSC but I put a plastic lid from a 5 gal. bucket over the top and sat my waterer on that. It has kept it ice free for over a week now and it's been down to 10 degrees here.