Here is a site for heating water passively.
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
I think a stripped hot water heater in an insulated box topped with glass so the sun can heat it up will do, just paint everything black.
if it get too hot shade it it some or paint...
I will be a new chickeneer soon. My wife and I will be closing on a 10 acre spot of dirt. The first thing i will do is put chickens. I( have been wanting chickens for about 2 yrs now, but scared to put them in my backyard. I just cant wait. I have been reading for a long time on chickens so...