Yes, they drink out of the top.
It is just behind the willow branches, inside the screen door that divides the chickens' space from the storage space.
This picture was taken last Feb, I think. It might have been January or March. You can see the snow on the windows.
I went with insulation rather than a heater. Vacuum is the most efficient insulation so I found 3-quart ice buckets for chilling wine. It works well down into the teens and single digits as long as the water is changed every 12 hours or so. It keeps the water cool in the summer, too.
If I had...