Sand dams are an ancient water-saving technique that is thousands of years old and could prove to save millions of lives from drought. They are constructed out of concrete barriers 1-5m high and filled with sand. When seasonal rains fall, water collects behind the dam. The sand acts like a sponge and filters the water and slows evaporation. Clean water can be drawn for up to several months after the rains have fallen through pipes underneath the dams or by digging a hole in the sand.

Simon Maddrell, the executive director of Excellent Development, won the major prize after pitching his idea to a group of experts.

The ancient technique was developed by the Romans in 400BC but is continuing to prove very effective today. Excellent Development has built 250 sand dams in Africa already, providing water for 250,000 people. According to some, these sand dams have the potential to give up to 3 million people access to clean water in the drylands of Africa.

This implementation would be of particular benefit to women because women do most of the farming in these African villages, and sometimes they spend up to 5-6 hours a day just collecting water. Sand dams close to their village would reduce this to just an hour a day.