Heated drinkers

Difficult to keep an eye on it if you're out at work all day though.  My chickens water freezes over withing about 2 hours of putting it out when the weather is very bad.

Buy a potting tray (black plastic) and put a small ball in it. The slightest breeze will keep the ball moving on the water and stop the ice forming. Empty in the evening and refill first thing. If needed get a camping water carrier to take fresh room temperature water the allotment.