For most people, having a open stream of sewage running past your backyard is a problem, not an asset. That how Keshav Tavre, who lives in Bhiwandi, India, saw it, until he decided to set up a homemade filtration system. With a series of walls and layers of soil, he was able to filter the sewage until it was clean enough to use to grow crops. Later, he sold water commercially do local dye industries.