Alain Gachet quit a lucrative career in oil to search for water underground. Colleagues told him he was a 'crazy donkey', but he eventually developed an algorithm that allowed him to 'peel the earth like an onion' and detect water beneath the surface. Soon, he was asked to train his talents to help pinpoint areas of life-saving reserves of water for desperate refugees escaping the conflict in Darfur.

Presenter: Jo FidgenProducer: Anna Lacey and Hetal Bapodra Editor: Munazza Khan

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