Tom Heap meets Darren Reynolds, a health and environment professor, who has developed a mini treatment plant that can turn dirty water into clean drinkable water.

The technology could be transported around the globe and put to use in places where clean water is scarce, such as in areas where there is a humanitarian crisis.

Costing The Earth discovers how the machine works and looks at other technology that could improve the water supplies of millions of people around the world.

Presenter: Tom Heap
Producer: Martin Poyntz-Roberts.