In lieu of the ad valorem tax authorized in paragraphs (a), (b), (c) and (d) of this subsection, the fees authorized in subsection (2) of this subsection and in Section 19-5-17 or any combination thereof, the board of supervisors may levy an ad valorem tax not to exceed six (6) mills to defray the cost of establishing and operating the system provided for in Section 19-5-17 on all taxable property within the area served by the system as provided in paragraph (a) of this subsection. Any board of supervisors levying the ad valorem tax authorized in this paragraph (g) is prohibited from assessing or collecting fees for the services provided under the system.