The back of the Aquaduct is a large water resevoir, attached via tubes to a 2-gallon tank on the front, which is removable for home use. As the user rides, the crank pushes water through a filter on it way to the smaller tank.
Editorial note: Whoa! You've found a super-old post here on BuzzFeed, from an earlier era of the site. It doesn't really represent where we are anymore, and may in fact be totally broken, but we're leaving it up as a part of our early history.