There are several different things you can try to keep your water from freezing. The black rubber bowls will allow the water to freeze. They are used by many because it is fairly easy to turn them over and stomp the ice out of them before refilling with water. Rubber bowls require that you go out and replace the water 2 or 3 times a day. These are used by those who do not have electricity to their coop or do not wish to use electricity.
Abriana mentioned using a heated bucket. Those work well with the horizontal, not vertical nipples. Vertical nipples freeze faster than horizontal ones. This requires electricity to the coop. I use a heavy duty extension cord to an outside outlet.
If you are using a metal font type waterer you could use the cookie tin method. This is putting a light bulb into a cookie tin and setting the waterer on top.
You can also use your own container. Some use a 5 gallon bucket, some use a large plastic container or jug with lid. I use a 10 gallon tote with lid. You can then use a stock tank deicer inside. Some people prefer an aquarium heater. With horizontal nipples this works very well. It had gotten down to -22 F here and the birds had thawed water.
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