More than 2/3rds of the world's population uses polluted water to fulfil its requirements. Physicist Ashok Gadgil and his team at the Lawrence Berkeley Laboratory, Berkeley, California, have devised a low-cost ultraviolet (UV) light system to tide over the problem. Fluorescent tubes -- free of the phosphor glaze which absorbs UV radiation -- in a steel box purify the water passing below by UV irradiation, 26 litres per minute. Since UV light cannot kill intestinal parasites like giardia, Gadgil recommends the use of a sand filter in endemic areas.