There is a lot of discussion on here on how to keep your water from freezing. I came up with this solution and installed it last night. I purchased a flat panel radiant heater from amazon.com for around $50. It is made to keep your feet warm under a desk and does not get super hot. As a matter of fact, some of the bad ratings that it received were that it doesn't get hot enough. Bad for keeping your feet warm but good for the coop! I mounted it on the wall with the brackets that came with it to stand it upright on the floor. Had to make a few modifications (drill some holes) in the brackets to mount them but it works great. It hasn't been tested in sub zero temps yet but I'll let you know. The plastic waterer does not touch it directly. As a side benefit, it does raise the temperature of the coop a few degrees. I have on order a Thermo Cube so the panel won't be on 24/7 when it gets warmer. The Thermo Cube will turn the panel on when the ambient temperature reaches 35 degrees and off at 45. These are also available on amazon for about $11.00 plus shipping. Not a super cheap solution but seems to be effective. I know they make a plastic waterer that plugs in but it gets bad reviews and I don't like to mess with plugs with wet hands. Hope this helps!