You can buy a solar chicken waterer that also keeps the water cool in the summer. It somehow stores heat collected during the day and keeps the water from freezing at night. It's only $35:
https://stores.myregisteredsite.com/user1249836/mm5/merchant.mvc?Screen=PROD&Product_Code=TC
https://stores.myregisteredsite.com/user1249836/mm5/merchant.mvc?Screen=PROD&Product_Code=TC