In 2009, twin NASA satellites – orbiting 300 miles above Earth, measuring changes in the mass of underground water in northern India – yielded disturbing data: Excessive irrigation practices were sucking the region dry. Even though rainfall had been slightly above average, millions of tube wells – like too many straws in the glass – were draining ground-water levels by as much as a foot per year, threatening farm output in the country's fertile breadbasket and raising the risk of a major water crisis. Over the past seven years, an amount equivalent to nearly three times the water in Lake Mead, America's largest water reservoir, had been lost.
"If measures are not taken to ensure sustainable groundwater usage," NASA scientists concluded, "the consequences for the 114 million residents of the region may include a collapse of agricultural output and severe shortages of potable water."
If renewable water supplies – rainfall in lakes, streams, and rivers – are like an annually replenished checking account, then ground water and deep aquifers are the savings. A few thousand years ago, when civilizations first branched out from rivers, they populated areas where they could draw from that savings in the form of ground water 20 to 30 feet below the surface. Globally, this was the norm until the 1950s, when fossil fuel energy became widely available to allow pumping water from ever-deeper depths. Ever since, humanity has increasingly lived beyond the margins of its renewable water supply.
In ancient fossil aquifers – in the Great Plains of the United States, the North China Plain, or Saudi Arabia – water levels are not recharged by rainfall. Elsewhere, as in northern India, ground water is used faster than it can be replenished. According to the United Nations, ground-water extraction globally has tripled in the past 50 years, during which time India and China's ground-water use has risen 10-fold.