Last year I used one of these:
I am wondering if this heat tape would work on the waterers. Any of you know?
This is what it says about it ....
It is hard to beat Flex Watt's dependability, cost effectiveness and ease of use. Flex Watt is ultra thin at just .012 inches thick and it's element is sealed in a tough flexible plastic so that it can be used in many different types of heating applications.
* Flex Watt Heat Tape features the following... Permanently sealed in a tough flexible plastic so that it can be used in many different types of heating applications.
* Versatility, the tape can be cut to any length, heating a very small amount of space or long and large areas.
* Exclusive and easy step by step connection instructions are included with your Flex Watt purchase.
You must use a thermostat to control the tape's heat level. A Cord with Attached Clip and Clip Protective Insulator Set is the only required equipment for each connection.
Foil Tape: Use the foil tape (available by the foot) to adhere the heat tape to most anything. You will need 2 feet of foil tape for every foot of heat tape as it will need to be run on both edges of the tape.