Keep them dry, and they can keep themselves warm. They are wearing down jackets, after all.
I don't have water in the coop at all. Less moisture in the air, less condensation. I do have a feeding station in the coop, as I want to have feed available "out of line of sight" for the pullets.
One thing I bought to help with winter was a heated water bowl. It's marketed as a dog water bowl, but it worked great for the chickens. It's out in the run. I don't have electricity in the run, so I used a heavy duty construction grade extension cord and plug it into an outlet in the garage.
I used clear shower curtains to make a wind block on the west (prevailing wind) side of the run, and wrapped around the SW and NW corners about 3 feet. That way, they had a good wind break and came out of the coop at least part of every day. (Not as much fun as
@3KillerBs bales of straw, but she's in NC and I'm in MI.)
I used heavy duty tarps over the metal frame that makes up my run, and it worked very well, but it was dark and gloomy in there. I had to make sure to keep the snow broomed off; while it was pretty strong, I was aware that a heavy, wet snow could bring it down.
We had one brutal cold snap of single digits below zero, air temps. I had read somewhere that chickens will eat snow for water. I saw that they weren't coming out at all, so I put a pan of snow just inside the door to the coop. Sure enough, there were beak marks all over it.