Our Homemade Solar Water Heater we built to heat the water for our Homemade Ofuro (Japanese Soaking Tub). You can learn how to build your own from this great website: Solar Water Heating. The Solar Water Heater we built can be found here: An Experimental Copper/Aluminum Solar Water Heating Collector. The only difference in ours is the dimensions. Ours was made on a 4′ x 4′ plywood base… because we built it in our apartment before we moved out to the mountains.