One person in six lives without regular access to safe drinking water, and more than twice that many lack access to adequate sanitation, according to the United Nations. Water-related diseases kill a child every eight seconds and are responsible for 80 percent of all easily preventable illnesses and deaths in the developing world. These alarming statistics have not escaped Dean Kamen's attention. The entrepreneur and quixotic inventor best known for the heavily hyped (and somewhat disappointing) Segway scooter has been working on what he promises will be a revolutionary new water purifier. Dubbed the Slingshot, Kamen's washing-machine-size device produces 10 gallons of clean water an hour on 500 watts of electricity. It uses heat to distill water—boil it, condense it and recycle the energy. The heat that it uses is captured from a new type of generator that, you guessed it, Kamen invented. NEWSWEEK's Brian Braiker spoke with Kamen about his mission to bring light and water to the world's poorest. Excerpts:

NEWSWEEK: You've been working on this for a few years. What's new now?
Dean Kamen: In a perfect world I'd say we're still probably a year away from being able to make reasonable quantities for testing and probably two years away for very high-volume production that will meet the needs of the world. We have been slowly but steadily improving it, making it simpler, cheaper, more reliable, able to deal with more and more different kinds of problematic kinds of water. We get more confident that we really have a neat little solution to a very big problem.

We're talking about two machines that work together, correct?
If you have a source of electricity, you only need one machine: the water machine. Of the billion-plus people on the planet who have no access to clean water and the billion-plus people who have no access to electricity, the overlap between those two populations is pretty large. Which means that if you make a water machine that, on the good-news side, doesn't need disposables—it doesn't need chemicals, doesn't need osmosis membranes, doesn't need activated charcoal, it doesn't need consumables—you sit and say, "That's really neat." But when you say that it does need electricity, you'd be wiping out a huge percentage of potential applications.