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 .