Droughts make matters worse, but the real problem isn't shrinking water levels. It's population growth. Since California's last major drought ended in 1992, the state's population has surged by a staggering 7 million people. Some 100,000 people move to the Atlanta area every year. Over the next four decades, the country will add 120 million people, the equivalent of one person every 11 seconds.

More people will put a huge strain on our water resources, but another problem comes in something that sounds relatively benign: renewable energy, at least in some forms, such as biofuels. Refining one gallon of ethanol requires four gallons of water. This turns out to be a drop in the bucket compared with how much water it takes to grow enough corn to refine one gallon of ethanol: as much as 2,500 gallons.

By Robert Glennon -- Washington Post

Updated: Mon, Aug 24th 2009 @ 1:49pm EDT