I'm in Ohio and thankfully it's not been that cold so far, I get out there at dawn break before the girls get up. I heat a kettle on the stove and use a metal watering can. I put some in their outside bowl some in their indoor waterer. Since we're averaging high 30's to 50's during the day it stays pretty thawed during the day.
I'd love to get a heated waterer, but there is no electric in the coop and most likely will be staying that way.