A billion people around the world face a stark choice - to drink potentially lethal water or nothing. Sometimes when faced with these huge facts, we can feel that there is nothing we can do to change them.

When I first heard the remarkable story of Pump Aid, I was reminded of something Margaret Mead, the American anthropologist, once said: “Never doubt that a small group of thoughtful, committed citizens can change the world. Indeed, it's the only thing that ever has.”

Pump Aid is the story of three thoughtful, committed Zimbabwean teachers who saw several students die after drinking contaminated water, and believed that they could make a difference. Ten years later, Ian Thorpe, Amos Chitungo and Tendai Mawunga's organisation has provided clean drinking water to one million people across Zimbabwe and Malawi via their brilliantly simple elephant pump. Brilliant because it can lift water from 50m, and produce a litre of water a second - enough to drink, cook with and even grow crops.

Simple because the pump uses nothing more complicated than rope and washers, so it can be fixed by the people who use it. Once a village's application for an elephant pump is successful, Pump Aid provides materials and expertise, and villagers help to construct the pump. This means that 95 per cent of the pumps are working at any one time.

Pump Aid wants to help people beyond Zimbabwe and Malawi, and establish clean water supplies for eight million of the poorest people across Africa. There can be no greater cause - because dirty water kills. At any one time, half of all hospital beds in developing countries are filled with people suffering from water-borne diseases. Women in Africa spend, on average, a quarter of their day walking to fetch water. Girls often help, and that means they do not have the time to go to school.

This tragedy of wasted potential was brought home for me when I visited the village of Kedida Gamela in Ethiopia in October. Because the rains had failed, women were forced to walk for five hours a day to reach the nearest source of water, a muddy watering hole, shared by animals and people alike.

While I was in Kedida Gamela, rain fell for the first time in months. It began to form huge, dirty puddles, from which I knew those villagers would be forced to drink, inviting disease that could kill them or their children. Millions of people face the same daily dilemma. An elephant pump would transform their lives.

Douglas Alexander is Secretary of State for international Development. Pump Aid is supported by the Times Christmas Appeal. Make a donation at timesonline.co.uk/timesappeal

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