Well, here is my idea for a non-electric way to heat my chickens' water this winter.  At a flea market this weekend, I bought a flat-bottomed metal bowl with bakelite handles.  It's about 6" across the bottom.  My plan is to keep it inside at night (because chickens dont drink when they're sleeping).  Each morning, I'll fill it with hot water and take it outside.  When it's cold, we'll have the wood stove going, and I'll keep a few of those decorative 4" river rocks on top of the stove, heating up. When I go out to visit my girls (which I do several times a day, just cause I love them!), I'll take two hot rocks and put them in the bottom of the metal bowl to keep the water thawed.  I'll take the cooled rocks back inside and reheat them.  (We have a soapstone stove, so the wet rocks wont damage the finish.) 
So that's the plan -- I'll let you know if it actually works!