For the past thirty years, rural villages in Bangladesh have relied on local hand-pumped wells to obtain clean water. Recently, many of these wells were painted red. Oversized Xs scream "caution" and "stop" to thirsty villagers. The reason? This "clean" water harbors dangerously high levels of naturally-occurring arsenic. The contaminated wells disproportionately affect the country's poorest citizens, injuring not only their health but their livelihood.

This isn't the typical story of dirty water killing the children of a developing nation. Nor is it the story of a country's effort to clean up its water and reduce the incidence of diarrheal diseases. Instead, this is the story of success's dark underbelly in one of Asia's poorest countries. In the mid 1970s, the international community claimed victory in Bangladesh, reducing child mortality by providing wells with clean water to 97 percent of the population. No one knew that they were simultaneously incubating the worst case of mass poisoning in history. Slowly, the international community is working to mount a response, starting by marking contaminated wells with a simple red 'X.'

Bangladesh is a country defined by extremes. It remains largely rural despite being one of the word's most densely populated nations. Almost half of the population languishes below the poverty line, and 82 percent of Bangladesh's poor live in rural areas. Each year, Bangladesh bears the brunt of numerous natural calamities: massive flooding during the monsoon season, short droughts during the main growing season, and the ever-present specter of tropical cyclones and tidal bores. Arsenic poisoning brings a new and chilling threat to an already overburdened country. Recent estimates suggest that 35 to 77 million people Ð between 25 and 55 percent of the total population Ð are at risk of drinking water contaminated by arsenic.

This development emerges from the shadows of an earlier, and not insignificant, success story at the beginning of Bangladesh's modern history. Born out of a brutal war with Pakistan in 1971, Bangladesh grew up destitute. At independence, nearly three-quarters of Bangladeshis were living below the poverty line or were drinking surface water. For those without wells to access groundwater or contraptions to collect enough rainwater to last through the dry season, surface water was the only alternative. But in Bangladesh, the surface water swarmed with cholera, typhoid, and a host of other water-born illnesses. More than 250,000 children were dying from these diseases each year.