We live on a parched planet. Farmers till arid pastureland, and policymakers fret over empty reservoirs, dry rivers and thirsty cities. And that only scratches the surface — literally — of the world's water problem. Subterranean aquifers, which amount to the world's reserve water tank, are also running dry. If this continues, the consequences could be dire, especially for water-stressed and fast-growing Asia.

Subterranean aquifers are repositories of water located deep underground, in permeable rock, soil or sand. And they contain about 100 times the amount of water found on Earth's surface, in streams, lakes, rivers and wetlands. If you're in central Africa, South America or some parts of Europe, you're probably standing just a few hundred meters above one.

Surface water resources, such as desalinated seawater or recycled wastewater, will not close the global gap — predicted to reach 40 percent by 2030 — between water supply and demand. So subterranean aquifers are increasingly being exploited for agriculture, power generation and daily use in fast-growing cities (urban Asia is growing at a rate of 120,000 people per day).