I've been mulling this over for, well, a year. Just got my first chickens this spring.
I can't run electric easily, and I only have three hens. They are in the MPC "Clubhouse" so I don't have a ton of room for a big waterer. Normally I use one of those hanging quart waterers. I was planning to swap it out regularly, but I work full-time so that's tough.
I *think* I may have figured something out. Here's my current attempt. A big black rubber feed bowl that holds about 1.5 quarts, with water in it. Inside, a plastic takeout container. Inside of that, water with one of those reusable hand warmers.
Before I leave for work, I snap the metal disc on the hand warmer. It warms the water in the plastic container, which warms the water in the bowl. The chickens can't peck at the hand warmer because it's in the container.
It won't last all day, but it lasts longer than the hanging waterer. We've been fortunate to not have too many below 20 F days so far, so I'll report back. But this just might get me through the short days so that I can go back to swapping waterers.