Thanks to all. I think bringing the waterer in at night is going to be the answer for me. I was worried about doing that because everyone I know says that you can't leave chickens without water, but if they're not drinking at night anyway, it shouldn't be an issue. Plus, the other option is them waking up to frozen water that they can't drink, so what's the difference?
I never heard about warm water freezing faster than cold...very interesting...I will keep that in mind.
Something about 600' of extension cords AND crossing the driveway is just too scary. If people can live without electricity, I am hoping that my chickens can as well.
I still think that some clever person should invent a solar water warmer, or a thermal blanket for those metal waterers. I think a lot of chicken lovers in the cold part of the country woud find them usefulwith or without electricity.
Thanks to all.