7 Solar Water Heating System Designs, by Michael Hackleman. "Solar-water heating systems got a real boost in the when tax credits were offered by state and federal programs to help folks make the investment.
Another version on rain gutter gardening. Want to grow a salad garden but have no room? Try gutters! Affix them to a fence, slope them for drainage, and voila! Of course,for this I'd need a backyard wider than a hallway.