I have a 5 gallon bucket with the watering nipple installed on the bottom inside my coop. It's been less then 20 degrees the past week in the day time so I've had to change the water 2 to 3 time a day! So I went to petsmart and got the smallest aquarium heater they carry, a 7.5 watt for about $13. I wrapped a piece of copper wire around it to keep it about 1in off the bottom. It works! The top gets iced over still but the nipples don't freeze. Just thought I'd share this for anyone who is going through the same problems I had.