2. Sewer rentals, charges, or rates may supplant or replace, in whole or in part, any monetary levy of taxes which may be, or have been, authorized by the board of trustees for any of the following purposes:
- a. To meet interest and principal payments on bonds legally authorized for the financing of sanitary utilities in any manner.
- b. To pay costs of the construction, maintenance, or repair of the facilities or utilities, including payments to be made under any contract between municipalities for either the joint use of water or sewage facilities, or for the use by one municipality of all or a part of the water or sewer system of another municipality.