I am just like chicmom, above.
I don't try to prevent water from freezing. Instead I have summer water buckets and winter water buckets. The summer size are 5 gallon buckets, the winter ones are 1 gallon size. They all have lids and carry handles, they all have poultry nipples on the bottoms (3 on each). In the winter time, a bucket of room temp water gets brought to the coop, and hung, the one already out there (long enough to freeze) gets brought in to the house for thawing/refilling for the next trip to the coop. Generally they get a bucket in the morning, and if it needs doing, another one mid afternoon, an hour or so before they will roost for the night.