Any county, municipality, or agency entering into any service agreement under section 13-2024 shall fix, maintain, revise, and collect fees, rates, rents, and charges for functions, services, facilities, or commodities furnished to its customers and users by and through its system as will be sufficient to:

(1) Pay (a) the cost of operating and maintaining the system and renewals or replacements thereto, including all amounts due and payable under such service agreement, and (b) the interest on and principal of any outstanding bonds or other indebtedness of the county, municipality, or agency relative to the service agreement, whether at maturity or upon sinking-fund redemption, which are payable from the revenue of its system; and

(2) Provide, as may be required by any resolution, ordinance, trust indenture, security instrument, or other agreement of the agency, for any reasonable reserves for such operating and maintenance expenses and for any margins or coverages over and above debt service.