Overview of the District Municipal Separate Storm Sewer System (MS4)

WASA operates a wastewater collection system comprised of "separate" and "combined" sewers. Since the early 1900's, sewers constructed within the District have been separate systems and no new combined sewer system (CSS) have been built.

Separate systems are comprised of two independent piping systems: one system for "sanitary" sewage (i.e. sewage from homes and businesses) and one system for storm water. In the District, approximately two thirds of the District is served by a municipal separate storm sewer system (MS4). The remaining one-third is served by a CSS. The CSS is outside the legal jurisdiction of the Storm Water Administration.

The MS4 system discharges into portions of the Potomac, Anacostia, and Rock Creek watersheds. The percentage of the Potomac, Anacostia and Rock Creek watersheds located within the MS4 are detailed in the Municipal Separate Storm Sewer System (MS4) Area by Watershed Map*.

To learn what watershed you live and weather you live in the CSO or MS4 area: Locate your watershed and type in your address.