All you need is legal access to a junkyard (or dump) to plunder parts such as the grill on the back of a refrigerator, some wood for the frame, a pane of glass, and a discarded rubber door mat. Yeah, eat your heart out, MacGyver.
This first-prize winner of our TreeHugger/Popular Science/Instructables Go Green contest also used duct tape to seal cracks, rather than the more-expensive caulk. The only thing he purchased new was a $3.76 air-pump hose from an aquarium store, because he already had the screws he needed on hand.
Our winner managed to heat a 5 gallon bucket of cold water to 170 degrees Fahrenheit on a day that averaged 76 degrees, thanks to some frugal ingenuity, gravity, and that big flaming ball in the sky. Learn how by following his step-by-step instructions. ::Instructables