Before development, San Francisco was covered by sand dunes, grassy hills and wetlands that absorbed rainwater, allowing it to enter the soil and replenish groundwater and streams. Today, paved and impervious surfaces such as buildings, streets, and parking lots cover most of the City and causes storm runoff to immediately enter the wastewater system. Storm runoff picks up pollutants like oil and debris that washes into our sewer system, which, during heavy rains, contributes to flooding and combined sewer discharges.

Cities around the world are taking advantage of stormwater management technologies often called Best Management Practices (BMP) and Low Impact Development (LID) to help reduce the impact of urbanization on the environment. These approaches mimic natural watershed processes by allowing stormwater to filter into the ground instead of entering our sewers through strategic placement of landscaping, gardens, and permeable concrete. These technologies offer many benefits:

·         Improve the efficiency of our wastewater system by reducing the amount of stormwater that enters our sewers 

·         Reduce the volume of combined sewer discharges

·         Remove pollutants prior to entering our wastewater system

·         Use rainwater as a resource

·         Increase vegetation and recreational areas 

·         Enhance neighborhoods and natural habitat

                 
In San Francisco, the SFPUC is actively pursuing ways to improve our wastewater system in a manner that enhances the environment, reduces pollutants from entering the bay and ocean, and minimizes impacts on neighborhoods. A major part of the sewer system master plan is to identify how “green technologies” can help address challenges facing the system, and LID approaches are a core element of all potential improvement alternatives. The SFPUC is also working with other City departments such as the Mayor’s Office of Greening, the Department of Public Works, and the Planning Department to pursue policy that requires new and redevelopment projects in the City to take advantage of stormwater management technologies. The policy will address watershed planning, urban design standards, evaluation of projects to assess opportunities for LID, technical assistance and demonstration projects.