Cheap and readily discarded clear plastic umbrellas are just the thing when you're caught off guard by a shower.

But the same qualities that make them so handy in a pinch are why they often end up, after the shortest of lifetimes, on the trash heap, adding to the mountains of petrochemical garbage blighting the environment.

Taking advantage of a "community currency" system already in place in Shibuya Ward, a group of university students in Tokyo has started a project to reuse discarded plastic umbrellas.