Man made islands are just for business and pleasure, they can serve a wide variety of functions including giving you a work out and purifying the water.

A new man made island design allows eco-conscious exercisers to synch your workout with a little river detox, then rehydrate with a cup of the fresh water you just filtered. This people-powered water purification island is designed by Jakub Szczesny as part of the synchronicity architecture and art festival in Warsaw, Poland. The premise of the poject is that it hooks up basic exercise machines to kinetically pump polluted water through four filters into overhead tanks that spill into a large drinking fountain at the end of the cycle.

This floating platform located on the Vistula River aims to empower citizens toward environmental clean-up, and apparently would work on any body of water with enough local bodies willing to pedal for their potables!

Source: Inhabitat