As the world population increases beyond 6 billion, one of the most fundamental resources for human survival, clean water, is decreasing.

Surface-water supplies often cannot meet the rising demands for clean water, leading to an increased dependence on groundwater in many parts of the world.

One of the new health issues raised by this is arsenic poisoning, which causes calluses on the palms and soles of feet, leading to skin cancers. The situation is especially severe in India and Bangladesh, where an estimated 36 million people are at risk.

Source: Science 296, 2143 (2002)

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Photo credit: WHO