In many parts of eastern India, Bangladesh and southern Pakistan, overuse of groundwater first brought the level of arsenic above the safe limit of 0.05 milligrams per litre of drinking water, as prescribed by the World Health Organisation. Now, as climate change reduces the rate at which rainwater seeps underground, the arsenic concentration is getting worse. When the problem was first diagnosed in 1983, 22 affected villages were identified in West Bengal. Now the number has gone up to 3,417 villages.