Untreated sewage leads to poor sanitation and disease around the world. Its effects are felt strongly in India, and Bangalore resident Tharun Kumar turned to cows for a solution.

With help from the Biomimicry Institute, he has designed and built 50 sustainable sewage plants that work in a similar way to a cow’s stomach. The system has no moving parts, so doesn’t require any power or people to operate it.

Voice: Patrick Aryee

Digital producer: Jennifer Green

Animator: Jules Bartl

With thanks to Tharun Kumar, ECOSTP and Dr Dai Grove-White, University of Liverpool

For more on this story, listen to 30 Animals That Made Us Smarter.