By Roland Buerk
BBC correspondent in Dhaka
Experts from around the world are gathering in Bangladesh for a conference on arsenic contamination of ground water.
Millions of Bangladeshis may be drinking unsafe water
Scientists estimate 85 million people in the country are drinking water that contains dangerous levels of the chemical.
It leads to severe health problems, including cancer.
The three-day conference is taking place at Dhaka Community Hospital, a world leader in the field of arsenic poisoning.
Scientists, doctors and representatives of aid
agencies will be discussing progress in the campaign to make Bangladesh's drinking water safe.
The conference has been organised by Professor Qazi Karuzzaman of Dhaka Community Hospital.
Most people in Bangladesh get their supplies from tube wells.
But across much of Bangladesh the water from underground is contaminated with naturally occurring arsenic, which causes skin and liver conditions as well as cancer.
It is contained in the sediments washed down the rivers that pass through the country before emptying into the Bay of Bengal.
The Indian state of West Bengal which borders Bangladesh is similarly affected.
But just one in five wells have been tested, and fewer than 10% of villages where arsenic has been detected are being supplied with alternative sources of safe water.