Experts say the depletion of groundwater is a major threat to food security and economic stability in India, China, the United States, Mexico, Spain and North Africa. In China, the agricultural use of groundwater has skyrocketed, causing water tables to drop in many places by a rate of 5 feet a year.

"The breadbasket of China - north of the Yellow River - has millions of people dependent on groundwater," said David Molden, deputy director general at the International Water Management Institute in Colombo, Sri Lanka. Water depletion is "sitting there like a time bomb."

At 19,000 square miles, Punjab state is just 1.5 percent of India's total territory, but its annual output of rice and wheat produces half of the grain distributed by the state to more than 400 million impoverished Indians, according to Gurdev Hira, an expert on soil and water quality at Punjab Agriculture University in Ludhiana.

And even though booming economic growth in recent years has placed India in the international limelight, more than 60 percent of the economy is directly or indirectly engaged in agriculture and 2 out of 3 Indians live in rural areas, experts say.