Non freezing waterers

This will be our first winter with chickens and guineas. I would like to hear and see (if possible) how you all provide water in the winter. Currently we have a 5 gallon bucket with holes drilled in the sides. The water level is controlled by a toilet float. It works very well. The chickens just pop their heads in a hole and get a drink. The holes at at their normal head level. The bucket is filled from a rain barrel outside the coop. Good for warm weather, but not when the weather temperatures are freezing.
Thank you.