I switch from water bottles to crocks in the winter. The water freezes over night, but I empty and replace the water in the morning and late afternoon. The rabbits dig/bite through the frozen surface of the water and get what they need until I change them out.
If you have an automatic watering system, I think some folks use heating strips.
The aquarium heater is set to 80 degrees, and is moving through the tubes at all times, so there is no freezing. And with the drinker valves so close to the moving, warm water, they should stay unfrozen also.
I go out 3x day with hot water to fill the crocks. My nursing does are in a barn kept just above freezing as they require too much water to get by with 3 refills a day.