The Lower Cass Watershed (LCW) is a 24.1 square mile portion of the Cass River Watershed, a sub-watershed of the Saginaw Bay Watershed located in Michigan's Eastern Lower Peninsula. The Cass River Watershed has a total area of 908 square miles. The LCW drains portions of three townships within Saginaw County. Only two of these townships are part of NDPES Phase II communities and subsequently members of the SASWA. 53.9 square miles of the LCW are within the SASWA area of responsibility. The LCW borders the Flint River Watershed, and meet at a confluence that forms the Saginaw River. The Saginaw River flows 22.3 miles northeast to Lake Huron, discharging into Saginaw Bay.

The Upper Saginaw Watershed (USW) is a geographic area of 53.9 sq. mi. in Michigan's Eastern Lower Peninsula. It is a sub-shed of the Saginaw Bay Watershed, which drains over 8000 sq. mi. touching 22 counties in Michigan. The USW lies within Saginaw County, including all or portions of eight cities and townships within the county.

The Lower Tittabawassee Watershed (LTW) for the SASWA is a 37.3 square mile portion of the Lower Tittabawassee Watershed, a sub-watershed of the Saginaw Bay Watershed located in Michigan's Eastern Lower Peninsula. The LTW drains portions of four municipalities and townships within Saginaw County. The LTW discharges into a confluence forming the Saginaw River. The LTW conveys its flow southeast through Saginaw County until it discharges into the Saginaw River. The Saginaw River then flows 22.3 miles northeast to Lake Huron, discharging into Saginaw Bay. 

The Swan Creek Watershed (SCW) is a sub-watershed of the Saginaw Bay Watershed in Michigan's Eastern Lower Peninsula. The watershed has a geographic area of 9.5 square miles in the Saginaw Urbanized Area. The watershed drains approximately 140 square miles. Portions of two townships in Saginaw County, James and Thomas Townships, lie in the urbanized area of the Swan Creek. The Swan Creek flows into the Shiawassee River, which meets the Flint, Cass, and Tittabawassee Rivers to form the beginning of the Saginaw River. 

Storm water discharges from a regulated MS4 to a surface water of the State in an urbanized area, as defined by the 2010 census, are subject to regulation under the National Pollutant Discharge Elimination System.  MS4 permittees generally include the following municipal entities: cities, townships, villages, county agencies, universities, and school districts.  The Michigan Department of Environmental Quality completed maps to identify MS4s located in an urbanized area that may require coverage under an MS4 permit.

Portions of the Midland urbanized area come into Saginaw County in Tittabawassee Township and are therefore regulated by SASWA. This area may grow when the 2020 census results are collected.