Municipal Separate Storm Sewer System (MS4)

A Municipal Separate Storm Sewer System (MS4) is a network of stormwater drainage systems, such as pipes and ditches, that cities and towns use to manage rainwater and melted snow. Unlike wastewater systems, MS4s do not treat water; instead, they direct it away from streets and properties to prevent flooding and water pollution. The goal is to control stormwater runoff, reduce contaminants entering local waterways, and protect community health and the environment. MS4 programs are often regulated by environmental laws to ensure cities manage stormwater responsibly.