(1) When a permit for a discharge from a combined sewer system is issued or renewed under this part, the department shall require as a condition of the permit that eaves troughs and roof downspouts for the collection of storm water throughout the tributary service area are not directly connected to the sewer system. The department may allow the permittee up to 1 year to comply with this provision for residential property and up to 5 years for commercial and industrial properties.

  (2) Subsection (1) does not apply if the permittee demonstrates to the satisfaction of the department that the disconnection of downspouts and eaves troughs is not a cost-effective means of reducing the frequency or duration of combined sewer overflows or of maintaining compliance with discharge requirements.

  (3) As used in this section, “combined sewer system” means a sewer designed and used to convey both storm water runoff and sanitary sewage, and which contains lawfully installed regulators and control devices that allow for delivery of sanitary flow to treatment during dry weather periods and divert storm water and sanitary sewage to surface waters during storm flow periods.