Whenever a municipality has pledged revenue to be derived from charges for connection with or for the use of a sewerage system to the payment of the principal or the interest of any bonds or notes, the water pollution control authority shall establish and, when necessary, revise such charges at rates which shall produce sufficient revenue for the punctual payment of the annual interest and amortization requirements of such bonds or notes and, together with any moneys available from other sources, for the fulfillment of any covenant or agreement which has been made by the municipality with the holders of any bonds or notes with respect to the operation of such sewerage system.