Count me in as another fan of heated dog water bowls. Last winter, it got down to sub zero for days on end and that's when I found out that the three-gallon heated waterer with the heated base and the heated fount block are recommended only to 15 degrees. It got a lot colder last winter - oh, man was it cold. The heated water bowl was a lifesaver.
Along this line, my observations of my chickens are that they prefer to drink out of an open container, like a dog bowl, rather than those inverted jug waterers, which I have and they use if they have to. The dog's water bowl in the yard is an open bowl and they'll leave their coop and head right for it and get a drink before they start their day of destruction - - uh, I mean, free-ranging, even though there's perfectly clean water in the run.
Also, I didn't keep the waterer in the house with them, too afraid of fire. (Look at the grim stories from last winter.) The dog waterer did fine outside in sub-zero. I did keep it away from moisture and the elements.
Mary