We're expecting temps down in the single digits going into next week, so I went to the local farm store today and picked up a tank heater. It's overpowered for what I need, but is thermostatically controlled. The one I got works as floating or submersible heater, and since I water using a 5 gallon bucket with poultry nipples in the bottom, I used the heater as a submersible. I'm taking my chances on using an extension cord, and will put electrical tape around the connection to keep it dry. Worth the $32 to have an easy solution to keeping liquid water 24/7 all winter for the girls. I also don't trust the aquarium heaters, since they're designed to work at higher temps. The one I have in my aquarium only sets between 70 and 88F, whereas the tank heater is designed to keep the water above freezing. I checked it after several hours of operation today, and the water was not warm at all (our high today was around 40 F).