In March, residents of Cape Town, South Africa stood in line for hours to buy drinking water at supermarkets or pump it from springs amid severe water shortages.
Cape Town isn't alone: One in four big cities worldwide already has overstretched its water resources, and global warming may increase the likelihood of prolonged dry spells in some regions.
Facing a future of increasingly erratic rains, water-stressed cities are looking for solutions. One alluring possibility? The capture and reuse of storm water. But the water infrastructure of most cities was built with a single problem in mind: flood prevention. In Los Angeles, for instance, the U.S. Army Corps of Engineers developed a massive network of concrete channels to divert storm water to the ocean after a massive flood in 1938 killed more than 100 people.
Urban water jockeys now are changing their views of storm water. Some see it as an untapped resource. As dry regions and even some wetter ones deplete their surface and groundwater supplies, researchers are investigating ways to replenish underground drinking water aquifers with urban runoff.
In cities especially, using the subsurface as a giant rain barrel makes sense, because it saves space. It also may be the only alternative in cities with Mediterranean climates where rainfall only comes during a few months of the year.
But there's a problem: The water that runs from a city's roadways and rooftops is dirty. Urban storm water can contain trace amounts of harmful contaminants from pesticides, asphalt, vehicle exhaust, road salts, grease and oil, consumer products and human and animal waste.
"We want to reuse storm water in a way that's not going to introduce drinking water contamination," Richard Luthy, an environmental engineer at Stanford University, told EHN.
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