Municipal Separate Storm Sewer System refers to a collection of structures designed to gather stormwater and discharge it into local streams and rivers. MS4 is short for, “Municipal Separate Storm Sewer System”, where the word “Municipal” refers to a unit of local government like a borough or a township, but may also refer to an organization responsible for the administration of a developed area. And the number 4 refers to the four words that start with the letter “S”; “Separ