An estimated 10 trillion gallons a year of untreated storm water runs off roofs, roads, parking lots, and other paved surfaces, often through the sewage systems, into rivers and waterways that serve as drinking water supplies and flow to our beaches, increasing health risks, degrading ecosystems, and damaging tourist economies. But cities of all sizes are saving money by employing green infrastructure as part of their solutions to storm water pollution and sewage overflow problems.