The amount of rainfall that soaks into the ground, evaporates into the air and runs off into low-lying areas depends largely on the level of urban development. In highly urbanized areas, only 15 percent of water is absorbed into the ground compared with as much as 50 percent (depending on soil conditions), in rural areas. And where does that excess water flow in urban areas? Well, it flows into sewers, degrades much-needed natural habitat or fills urban streams and rivers. It also picks up and carries tons of pollutants with it as it passes over the ground.

The Water Cycle

Polluted Runoff

Water Quality Initiative
Milwaukee Metropolitan Sewerage District
August 8, 2008