This is on my top ten list of tools we've covered. Dawn's post on Kid Energy introduced us to the work of the South African company Roundabout, whose work is so brilliant I should just Dawn's piece it speak for itself:
South Africa's Roundabout has devised a way to harness the energy generated by kids playing (ingenious in itself), as they spin on an outdoor merry-go-round. Carrying water several kilometres per day results in hours of lost employment, and widespread use of poor-quality water; this is a win-win alternative... "The children push the merry-go-round again and again. As they run, a device in the ground beneath them begins to turn. With every rotation of the merry-go-round, water is pumped out of a well, up through a pipe, and into a tank high above the playground. A few feet away from all the fun, students in uniform turn on a tap. Clean, cold drinking water pours out."
And don't forget the seesaw water pump from Gaviotas, Colombia.
I've always wanted to harnessl the energy from people running on treadmills in New York City.