Leslie, the hens in your coop probably kept their water warm even when the temperature outside dropped below freezing.
I read of a small CSA farmer in the Santa Cruz, California, area. She penned her chickens in large runs with tropical fruit trees in them. In winter she would cover the whole thing with plastic. Said the heat from the chickens would give her about 6 degrees of frost protection, which was enough to prevent damage to her fruit trees. (Santa Cruz doesn’t get very cold unless you go east into the mountains.) —Bill Nunes, Gustine, California