Eye witness

Bangladesh's devastating floods may be receding, but they leave in their wake a greater problem - ensuring a safe water supply for the largely rural population.

Health problems linked to polluted water have led to hundreds of deaths and more than a quarter of a million people have suffered from diarrhoea. The shortage of safe drinking water is becoming acute, with 300,000 of the country's tube wells already damaged.

The wells, many sunk with international aid agency money, were designed to replace the shallow wells and surface water supplies which were responsible for chronic disease and sporadic cholera outbreaks.

Tragically, the solution brought even more insidious threats to the country's 100 million inhabitants - high natural concentrations of arsenic in water drawn from aquifers in the Ganges delta. The effects are seen in serious skin conditions and characteristic cancers in the past few years . Soon one in ten deaths in the south of the country could be from arsenic-related cancer.

The risk from the naturally occurring arsenic has been described by Dipankar Chakraborti, of the school of environmental science at Jadavpur University, who began his investigation in West Bengal before the enormity of the crisis was discovered across the border in Bangladesh.

John Whitelegg, of the school of the built environment at Liverpool John Moores University, says the tube well programme should be abandoned. Just back from Calcutta where researchers have constructed a hypothesis for the contamination, he rules out easy solutions.

"When, after 20 years of enthusiastic investment in a major water supply technology, you find the technology is not only not working but threatening terrible health consequences, you have to make a switch."

The technology exists to treat surface water cheaply and safely, Professor Whitelegg said. "The problem is that they are still digging tube wells - international aid agencies are still advocating the sinking of tube wells."

Other academics challenge the view that the well water cannot be made safe. Over the past two years researchers from the hydrogeology group at the University College London department of geological sciences have collected evidence to support an alternative hypothesis. Senior lecturer Willy Burgess says that the arsenic is related to iron in solution in the groundwater where chemically reducing conditions in the sediments coincide with accumulations of arsenic-rich iron hydroxide particles. Filtering out the iron is easy and the arsenic is "susceptible to a relatively cheap and simple treatment process".

Studies conducted with hydrogeologists at Dhaka University point to ways of predicting where and how deep wells should be sunk to avoid the contaminated sediments.

Dr Burgess says: "Surface water is out of the question because of the multiplicity and widespread occurrence of epidemics of water-borne diseases. If we can come to grips with the arsenic problem and solve it then groundwater becomes by far the safest option for the vast majority of Bagladeshis."