People who leave contact lenses in while washing their face risk a potentially blinding eye infection. Although rare, the disease is extremely painful.

A single-celled organism called Acanthamoeba, which can cause severe ulceration of the cornea, may be lurking in cold water storage tanks.

Consultant ophthalmologist John Dart, from Moorfields Eye Hospital in London, told the magazine New Scientist: "It's a ghastly disease. It's very resistant to treatment and difficult to eradicate."

Only about one in 30,000 contact lens users in the UK contracted the disease, but this rate was 15 times higher than that in the US.

Until recently, regulations required all homes in the UK to have a cold water storage tank. Mr Dart suspected that water in these tanks could be a breeding ground for Acanthamoeba after analysing DNA from organisms found in eight patients and their water supplies. Six were identical, indicating that the water supply was the source of infection.