India, Aug. 22 -- "What is lead," Gitanjali Rao swallowed the last of her pasta and asked her parents.

She was nine years old and had just heard about the water crisis in Detroit, Michigan, on the news. Children in parts of that city, not that far from her home in Lone Tree, Colorado, were drinking water contaminated with lead, and nothing was being done about it.

Shouldn't she at least try to help?

By the age of 11, she had taken her first steps to do so, designing a home-test kit that could potentially analyse water in real-time, to let families know whether it was contaminated or safe. The kit would be made up of carbon nanotubes that sent water-quality readings, via Bluetooth, to an app.

"I read this MIT article that said scientis...