(a) The board shall prescribe and collect reasonable rates, fees, tolls or charges for the services, facilities and commodities of any system, shall prescribe penalties for the nonpayment thereof and shall revise such rates, fees, tolls or charges from time to time whenever necessary to ensure that any system shall be and always remain self-supporting.
(b) The rates, fees, tolls or charges prescribed shall be such as will always produce revenue at least sufficient to:
(1) Provide for all expenses of operation and maintenance of the system, including reserves for the expenses;
(2) Pay when due all bonds, notes and interest and premium thereon for the payment of which such revenues are or shall have been pledged, charged or otherwise encumbered, including reserves therefor; and
(3) Provide for the extension or improvement of the system; provided, however, that the authority shall charge equal rates to the county, the districts and any municipality hereafter entering into such an agreement with the authority as provided in § 64-1-1218. This subdivision (b)(3) shall apply to the rates charged for the provision of services as outlined in § 64-1-1204(7).