I installed a DIY system using PVC pipe with nipples several months ago. It has worked well to an extent, though the hens spill a lot of water when drinking. It is still quite worthwhile because at least the water is always clean. Now, to address the point at hand: keeping the water from freezing. I recently purchased a fifteen foot electric pipe heating cable and wrapped the pipe all the way to a five gallon bucket which is on the other side of a partition. The cable has a thermostat and turns on and off when needed. So far it has kept the water from freezing. However, the lowest the temperature has dropped is somewhere near 26F. Colder temps are expected in the coming week so I will post a followup. Here is a pic taken before I added the heat cable.
Today I set up another DIY heater for the younger hens in the second partition. I made it with a concrete block, scrap wood, etc. The light bulb is only a 40W, but it is one of the larger round ones. I tested it the other night on my front porch with temp about 28F. It didn't freeze so I put it together and installed it today. When the temp drops I will find out how well it works also. Now, these two systems are both dependent on having an electrical supply. My problem is my water supply is about 150 foot away. I have hoses running to the coop, but will not be able to use them in freezing weather.
The light is away from the plastic so I don't believe it creates any hazard. The wiring goes directly into the partition so the chickens can't get to it. The container is secured by the boards in the back and a restraining twine around the front. Makes a pretty neat nightlight also.
And I had to have my lawn tractor tires filled with liquid and add wheel weight and chains to help insure that I can fill my two 6 gallon water containers and make the 100 foot+ trip to the coop, which is down a pretty good grade. I don't know if I have answered any of the questions, but thought I would express my plan of action. Will follow up as the nights get colder.