In the early 1970s the United Nations Children's Fund (UNICEF) and the Bangladeshi government embarked on a massive program to install hundreds of thousands of groundwater wells. They were to provide safe drinking water for the 125 million people of Bangladesh, who long relied on surface water that was often laden with lethal amounts of bacteria. Thanks to that initiative, today some 12 million wells supply 97 percent of the drinking water, was sparing the desperately poor country the 250,000 deaths from waterborne illness that used to occur every year.

But the wells have left the Bangladeshi people in an untenable position: although the groundwater has no deadly pathogens, it does harbor high levels of arsenic, which has caused at least 7,000 deaths since the early 1990s, say local officials. And uncounted thousands bear signs of long-term arsenic poisoning. "It is a gargantuan tragedy that nobody's seen anything like before," says geochemist H. James Simpson, Jr., of Columbia University, who has traveled to Bangladesh twice this year.

 Arsenic doesn't flavor, color or scent the water. "It has all the sensory impressions that would say to you, 'This is good water,' " Simpson explains. And, unlike pathogenic surface water, arsenic-tainted groundwater doesn't sicken you right away. One can ingest low doses of arsenic for eight to 14 years before white or black spots, called melanosis, start mottling the skin. If the poisoning continues, scaly, leprosy like skin lesions then encrust the palms and soles eventually rots into gangrenous ulcers. Finally come renal diseases, cancers-particularly of the bladder and lungs-and death.

 Occurring naturally in rock and soil, arsenic is not an uncommon problem around the globe. The World Health Organization's standard for arsenic in drinking water is no more than 10 parts per billion. The current U.S. standard is 50 ppb, but the Environmental Protection Agency wants to lower it to five ppb. The Bangladeshi standard is also 50 ppb, but wells there have tested at levels as high as 4,000 ppb, reports Dipankar Chakraborti, head of the School of Environmental Studies at Jadavpur University in Calcutta.

 In response to the crisis, the Bangladeshi government, which officially acknowledged the problem in 1995, has urged citizens to drink only boiled surface water and water from deep wells-those that descend more than 300 feet into a lower aquifer. (Wells typically go down 50 to 250 feet.) "Deep wells are providing safe water," says A. Mushtaque R. Chowdhury, a research director at the Bangladesh Rural Advancement Committee. "But we don't know how long they remain safe. And these wells are expensive compared to any other option."

 Simpson and a multidisciplinary team of 23 others may have found a more cost-effective alternative. In March the researchers began testing 5,000 wells in a region east of Dhaka, the capital city. These tests marked the start of a five-year project meant to examine the crisis based on geological, hydrological, health and social surveys. Besides finding 60 percent of the wells contaminated, they discovered, somewhat surprisingly, that water from shallow wells-those no more than 30 feet deep-contains little arsenic.

 One reason, according to team member Yan Zheng of Queens College, can be attributed to a well-known chemical fact about arsenic: it can be locked up in iron-oxide sediment in oxygen-rich waters. Filtering the water through, say, fine sand, was thought to remove arsenic-laced sediment. But experiments showed that this simple method, probably because of other compounds in Bangladeshi water, did not lower arsenic concentrations to a safe level, according to George Korfiatis of the Stevens Institute of Technology.

Without testing equipment, says co-principal investigator Alexander van Geen of Columbia University, "I would go for a shallow well that doesn't have iron visibly precipitating," meaning that the water doesn't turn yellowish or reddish when exposed to air. Preferring water without the iron that can hold arsenic may seem illogical, but van Geen reasons that if no iron has leached from underground mineral surfaces, then, quite likely, neither has arsenic, because both are often released into groundwater under similar low-oxygen conditions. Further research is needed to corroborate the team's findings.

 Phase two of the Columbia project began in July, when the health group returned to tell each family the arsenic level of its well. Unfortunately, the team lacks funding for a full-blown social-scientific study of people's water-drinking and well-digging behavior. "Here you have an epidemic, and they're still drilling wells," laments Columbia's Joseph H.Graziano, who notes that out of the 5,000 wells surveyed, some were just 15 days old.

"You pay someone a few bucks, and they'll do it." A first step in the epidemic could be a matter of sharing information. "If we can find the man who drills those wells and tell him what depth to drill," van Geen speculates, "perhaps we could deal with the problem like that."

--Kimberly Masibay

KIMBERLY MASIBAY is a science and environmental journalist based in New York

For more information on this issue, see http://www.dainichi-consul.co.jp/english/arsenic/