In the past decade drought has marched across much of the globe, hitting China, the Mediterranean, southeast Australia and the U.S. Sun Belt. The amount of water used by humans has tripled since 1950, and irrigated cropland has doubled. About one-fifth of the world's population lacks sufficient water, a figure that could reach 40 percent by 2025 by some estimates, in part because of growing world economies. In the poorest societies more than a billion people lack access to clean water, and dirty water kills 5,000 children -- enough to fill 12 jumbo jets -- every day. By century's end drought is expected to spread across half the Earth's land surface due to climate change, causing hunger and higher food prices. The United Nations says it would cost an extra $10 billion or more annually to provide clean water and sanitation for all. Some recommend privatizing water supplies, while others suggest that charging more for water to encourage conservation would help to avoid future crises.

Peter Behr recently retired from The Washington Post, where he was the principal reporter on energy issues and served as business editor from 1987-1992. A former Nieman Fellow at Harvard University, Behr worked at the Woodrow Wilson Center for Scholars and is working on a book about the history of the U.S. electric power grid.