Minnesota here hit -20 a few times last winter. I'm changing up my system, too. I plan to copy what my friend successfully does, which is to keep one of those rubber bowls with a birdbath heater in it. I'll rotate two. I plan to keep it in the run rather than the coop. Last winter during those cold snaps I made 3 and 4 trips out to the coop daily because I couldn't keep the water from freezing. I had the cinderblock with lightbulb setup. The bottom tray of water didn't freeze very often, but it got solid in the holding tank and couldn't descend. I liked how clean it was so that's how I'm doing it this summer (no bulb) but in the winter I have to find a better way! I was considering the 5 gal bucket with a birdbath heater inside and the lid loosely set on top and then screwing spigots in...like these
http://www.cornerstone-farm.com/equipment/poultry-float-valve-226
pretty inexpensive and solves the fowl (foul) water problem