Green for less: Ma Yanjun's beer bottle water heater
One of the most basic needs is clean water. To that end, my buddy Nick, who used to be a Peace Corps worker in Cape Verde, helped develop a low-cost still that uses solar power to de-salinize water. The prototype cost about $200 to make, but future models should be much more cost-effective. Best of all, it was constructed of locally-available materials. Here's a little video about it. In addition to addressing the problem of fresh water, which is a major issue in Cape Verde, he created something that can be endlessly replicated (and improved) by the people who need it.
Last year, Ma Yanjun, a carpenter in Qiqiao village, in China's Shaanxi province, came up with a similarly simple, ingenious idea that provides a basic need. Upset that his mother couldn't get a warm shower, he constructed a solar water heater out of old beer bottles and pieces of hose. Water heats as it slowly flows through the bottles and hoses; by the time it gets to the shower, it's comfortably hot.
Although simple and inexpensive, Yanjun's heater enables all three members of his family to have a hot shower every day. The idea has caught on, and he helped construct similar heaters for twenty other families in his village. While I haven't been able to find a plan for his water heater, the Department of Energy has a resource page for people interested in solar water heaters. They suggest that interested parties should hire contractors to build the requisite equipment, but I'm willing to bet that there are a few home-grown Ma Yanjun's out there who are already thinking about how to make a cheap American water heater from recycled parts!