In my large chickens' coop, we have a heated dog water bowl that I put on a platform 3 feet up so sawdust doesn't get kicked into it.
In the banty coop, I keep a round metal bowl on a slightly elevated stand (made by attaching the round metal frame from the top of a lampshade to some pieces of wood) with a "stool" for the chickens to stand on next to it while they drink. Sometimes I run a heat lamp in that coop (You can plug it into a timer so it only runs part of the day).
A really good idea a friend taught me was to 
put a dish of snow in the coop for the chickens to nibble on as well, between replenishments of fresh water. It helps keep them hydrated more consistently and for some reason they just LOVE nibbling on snow anyways, even when water is available.
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LATER NOTE: I have since heard conflicting info that said snow will make them more dehydrated. That doesn't seem logical to me, however. I'm thinking as long as they regularly do get actual water, and have sufficient feed to keep their bodies warm, that snow would be a hydrating substance for them to much on.
		
		
	
	
  Will the real answer please step forward?