65 ILCS 5/11-141-1
When used in this Division 141, "sewerage system" means and includes any or all of the following: a sewage treatment plant or plants, collecting, intercepting and outlet sewers, force mains, conduits, lateral sewers and extensions, pumping stations, ejector stations, and all other appurtenances, extensions or improvements necessary or useful and convenient for the collection, treatment, and disposal, in a sanitary manner, of sewage and industrial wastes. The term also includes the disconnection of storm water drains and constructing outlets therefor, where, in any case, such work is necessary to relieve existing sanitary sewers of storm water loads, in order to permit the efficient operation of such sanitary sewers for collection, treatment, and disposal of sewage and industrial wastes.
65 ILCS 5/11-141-1