Municipal Separate Storm Sewer System (MS4)

The following link presents the definition of municipal separate storm water sewer system (MS4) as taken from federal rules.

TCEQ - Municipal Separate Storm Sewer System (MS4)

First, a separate storm sewer system includes ditches, curbs, gutters, storm sewers, and similar means of collecting or conveying runoff that do not connect with a wastewater collection system or treatment plant.

Second, to be a "municipal separate storm sewer system" (MS4), the system must be owned and operated by a public agency, for example:

  • a city or town
  • a municipal utility district, flood control district, or other special district
  • a county
  • a state or federal agency.

These can include municipalities and local wastewater districts, state and federal departments of transportaion, universities, hospitals, military bases, and federal correctional facilities.

MS4s are categorized by the size of the population they serve.
Type of MS4
Population Size (Based on the U.S. 1990 Census)
Greater than or equal to 250,000
Between 100,000 and 250,000
Less than 100,000