Storm water runoff has traditionally been handled on a localized, piecemeal basis with the goal of minimizing localized flooding and erosion by moving the water down stream in as expeditious yet benign manner as possible. This approach has resulted in many concerns, ranging from localized "parcel level" problems of erosion and minor overflows to major regional flooding issues. This approach has resulted in large public expenditures, property damage, and even loss of life.

When rain water falls to the earth in a natural setting it typically hits "green surfaces" called non-impervious such as grass or other vegetative ground cover. In developed areas, it falls on green surfaces but also on hard surface (impervious) such as parking lots, rooftops, driveways and sidewalks. When it hits a "green surface" much of the water is absorbed into the ground. When water hits and then runs off hard or impervious surfaces, it picks up contaminants such as oils, grease and tire particles and then under the current approach is piped to nearby streams.