I use 3 different methods to keep our chickens water from freezing. I live in Nova Scotia, Canada and it can get quite cold here. Before that I lived in the northern tip of southern Ontario, Canada so we have had several experiments over the past few years.
1. Hang a heat lamp light right over the metal waterer. Pros: Keeps the water thawed unless the temperature is ridiculously low. You can put it on timer to come on after you fill your water in the evening until morning when the days warm up the coop enough. Cons: Works best with metal containers. It stays on all the time and uses the most electricity, so your power costs are higher than my other methods. Water can get too warm which can upset the birds. If the light bulb burns out and you don't know the water will freeze.
2. Purchase a heated waterer (we bought one from the local Co-op). Pros: Just plug it in and forget about it because it only comes on as needed. Cons: The fill hole is small and at the bottom of the waterer.... it's a REAL pain in winter... especially if you don't have water to your coop. They are a bit more costly than the third method (although cheaper than the first overall).
3. At your local nursery, get a heated seedling mat. Pros: It only comes on when you need it. You can put either a metal or a plastic waterer on top of it. It's safe & waterproof. The power cost is minimal. The seedling mats are the same price or lower as the heated waterers. If it's larger than the waterer, the hens can take advantage of the additional warmth of the extra space on the pad if they need it (especially good if you have young).
Hope this helps!
Didi
