I have a heated base. I got one from TSC al little less then $40. Im a first timer so I went with this option after hearing good things about them. It has an internal thermostat that kicks on at 35 degrees. I was worried that it would be hot to the touch but it is not. Had several nights in the twenty's here in Michaigan already this fall. Has worked like a champ. of course this all depends if you have power to your coop. I used a heavy extension cord plugged into a GFI outlet. Also heard about some type of heavy rubberized bowls as well but these just make it easier to break the ice up and you would have to refill several times a day.
I have a heated dog bowl I got at Wal Mart for $20. If you don't have power out to your coop, make sure you use a heavy duty outdoor cord.
I have heated bowls as well. They are available from 1 quart to 1 and 1/2 gallon size. If there is no electricity just us a rubber dish (TSC) and break the ice periodically. They don't seem to drink as much in the winter when there is snow on the ground. I can use a gallon size bowl in the winter but use a 3 gallon waterier in the summer.
