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A cheap filter that could improve the lives of millions of people in developing countries by removing toxic arsenic from water was unveiled last week by UNESCO.

The UN Educational, Scientific and Cultural Organization launched the filter on 13 October at its headquarters in Paris, France.

The filter, developed in the Netherlands at the UNESCO-IHE Institute for Water Education, has been undergoing tests in Bangladesh since February 2004.

The researchers say one filter can produce 100 litres of arsenic-free water a day — enough for 20 people — and will need replacing after about one year.

Arsenic in groundwater threatens human health in several countries, including Argentina, China, Ghana, India and the United States.

The problem is greatest in Bangladesh, where tens of millions of people drink contaminated water, and where long-term exposure to arsenic has caused skin disease and high rates of cancer.

The filter uses sand coated in iron oxide to absorb arsenic from water passing through it. Groundwater treatment plants produce such sand as a by-product and it can be recycled at virtually no cost, say the researchers.

"Our partner organisation in Bangladesh produced a few prototypes based on our design for US$35 per unit," says Branislav Petrusevski, the project's director.

He says mass production would significantly reduce costs, adding that that "no chemicals or power supplies are required, so overall treatment costs will be very low".

Petrusevski told SciDev.Net that his team would work with Bangladeshi organisations to distribute and maintain the filters, teach people how to use them, and dispose of the contaminated sand they produce.

"Small treatment systems like the UNESCO arsenic removal filter are very important," says Bas Heijman, a researcher at Kiwa Water Research, the Netherlands.

Heijman points out that supplying treated mains water to villages is often beyond the means of developing countries.

Richard Meganck and Andras Szollosi-Nagy, directors of the UNESCO's Institute for Water Education and International Hydrological Programme, used the filter's launch to call on donors to support its mass production.