We get below zero at night about 1/2 of the winter. And this year we had several days where the highs did not get to 30*. I have a 5 gallon bucket with nipples in the bottom. To keep it liquid in the winter I put an aquarium heater on the bottom of the bucket (it MUST always be covered with water or could start a fire, otherwise use a bird bath heater) and I never had any problems all winter. I normally have a garden hose connected to the bucket in nice weather. In the winter I just take out a gallon of water with me to keep the bucket full whenever I go to the coop 3-5 times each day.