World Premiere Keith Anderson, Director of the District Department of the Environment, is an advocate of green, or vegetated, roofs to help contain rainwater and reduce the volume of storm water runoff. That’s because runoff collects oil and grease from roadways, nutrients from lawn fertilizers and bacteria from pet waste as it flows into our rivers and streams. Green roofs also filter air pollutants from the rainwater and save energy in buildings. Anderson explains why green roofs are especially effective in Washington, D.C., and what his Department is doing to encourage them.