Never mind those ginormous dam-based hydroelectric generators -- we've got a much smaller version that you can actually use in your backyard. The Pico Hydroelectric Generator was installed within a 5-gallon bucket by Sam Redfield in order to convert the energy from "existing gravity fed irrigation, fresh water, or waste water systems" into usable electricity that can juice up your cellphone, DAP, portable fan / water-bottle combo, etc. Regrettably, there's not a whole heap of details beyond that, but you can check out another angle in the read link below.