Mich. Comp. Laws § 123.351

Sec. 1. The words "water supply system and/or sewage disposal system" as herein used shall include either or both of such systems or a combined water supply and sewage disposal system. The term "water supply system" shall include all plants, works, instrumentalities and properties used or useful in connection with obtaining a water supply, the treatment of water and/or the distribution of water. The term "sewage disposal system" shall include all sanitary sewers, combined sanitary and storm sewers, plants, works, instrumentalities and properties used or useful in connection with the collection, treatment and/or disposal of sewage and/or industrial wastes.