Arsenic is so common in groundwater in Bangladesh, Nepal, western India, Myanmar, Cambodia and Vietnam  all heavily populated countries in the flood plains draining the Himalayas  that their drinking water has been called “the largest poisoning of a population in history.”

But a recent study in Science magazine suggests simple well-drilling techniques that could lower the risk. The arsenic comes from eroding Himalayan coal seams and rocks containing sulfides; it is released into the groundwater only under certain chemical conditions deep underground. Some of those are affected by human activities, including pumping out huge volumes of water for irrigation. Different-colored sands may indicate how likely an aquifer is to be dangerous: rusty orange sands full of iron oxides often have less dissolved arsenic in the water around them than gray-colored sands do. Any village may have many orange and gray layers at different depths underneath it, and villagers may unknowingly live near both safe and dangerous wells. But testing is usually inadequate.

Therefore, the authors  geologists from Stanford, Columbia and the University of Delaware  suggest that wells for drinking water should be drilled in deep orange sands and connected to low-pressure hand pumps, while wells connected to high-pressure pumps for crop irrigation should be kept out of those deep aquifers so they do not empty them of safe water, which would cause arsenic-laden water to migrate downward into them.