Bike-powered water purification--3 tons in 10 hours has a story about a setup that uses a bicycle to provide the power to purify water for developing countries or disaster-stricken areas:

It works like this. You park up next to a muddy river or dubious looking lake. Lower a hose into the water, hitch the bike up on its stand, and climb back on. The rear wheel is kept off the ground, and the pedals now power a pump. Water is forced through a primary filter before moving on to an activated carbon filter, like the one you may have in a Brita jug at home. Finally, the water passes through a “micro-filtration membrane filter” before being stored in the vessel of your choice.

The CycloClean can process three tons of water in ten hours (you might want to take turns riding it). That's enough to supply 1,500 people for one day.

Manufacturer's web site is here.