While oil shortages grab the headlines, water scarcity is creating at least as many headaches around the world. The most dramatic conditions are in Asia, where the world's two megacountries, China and India, are grappling with deepening and unsolved water challenges. China's great northern plain, home to more than 200 million people, is generally subhumid or arid and depends on unsustainable pumping of underground aquifers for irrigation. The Yellow River has been diverted to the point that it no longer flows to the sea. Meanwhile the water tables of Beijing and other large northern cities are falling dramatically as a result of the pumping of groundwater.

Similarly, southern India is drought-prone, and southern states scramble after river flows that cross state boundaries. When the rains are poor, upstream states such as Karnataka turn off the water flow to downstream states such as Tamil Nadu, with brutal consequences for farmers and communities. In northern India, tens of millions of bore wells are depleting groundwater much faster than it can replenish, just as in China. Such problems are, of course, not limited to developing countries. Scarce river flows are bitterly contested among U.S. western states and between the U.S. and Mexico. A considerable portion of U.S. agriculture in the Great Plains depends on the vast but depleting Ogallala aquifer.

Continued population and economic growth will put still greater pressures on freshwater supplies. At this point, further claims on rivers and aquifers are often a zero-sum game: more water for one region means increased water scarcity and ecological destabilization elsewhere.

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