Here's one way: harvest some of the energy from the water and use it for power. A team of researchers in South Korea have created a transducer that translates water motion—from toilets, raindrops, or other water-based uses—into electricity. The technical side is wonky, but essentially, by using the motion from a tiny droplet of water—30 microliters—the team was able to power a small green LED. It's a proof-of-concept demonstration, but scale up to a flushing toilet or a rainstorm, and you can see the appeal.