I have two bowls. They are some of the heavy ones.

I change the bowls every morning and evening. One is outside for the rabbits. The other is inside and warms up (room temperature). It gets warm enough to hold the water liquid for approx. 8 hours.

To avoid the surface of the water in the bowl freezes I add a table tennis ball. Because of the balls moving the surface stays most part liquid.

Drinking bottles are not suited for freezing temperature. The water freezes in the pipe and the liquide from the bottle could not get through. And the (most time) metal part to lick on could hurt the rabbits mouth. Wet things (like lips or tongue) freeze to cold metal. So the skin will be injured.

If it gets very cold one could add bottles with warm water under the water bowl. The water in the bowl should not be filled in warm because this could harm digestion of the rabbits.

I have two bowls. They are some of the heavy ones.

I change the bowls every morning and evening. One is outside for the rabbits. The other is inside to warm up (room temperature). It gets warm enough to keep the water liquid for approx. 8 hours.

To avoid the surface of the water in the bowl freezing I add a table tennis ball. Because of the ball's movments the surface stays mostly liquid.

Drinking bottles are not suited for freezing temperatures. The water freezes in the pipe and the liquid from the bottle cannot get through. Licking at the (usually) metal part could hurt the rabbit's mouth. Wet things (like lips or tongue) freeze to cold metal. So the skin will be injured.

If it gets very cold one could add bottles with warm water under the water bowl. The water in the bowl should not be filled in warm because this could harm digestion of the rabbits.