If bonds or notes are issued by a board, the board shall establish, impose, and collect rates, fees or rentals for the use of and services provided by the residence halls and dormitories, including dining and other incidental facilities therefor, at the institution on behalf of which the bonds or notes are issued, shall adjust the rates, fees, or rentals from time to time, in order to always provide net amounts sufficient to pay the principal of and interest on the bonds or notes as they become due, and shall maintain a reserve. The board may pledge a sufficient amount of the net rents, profits and income derived from the operation of residence halls and dormitories, including dining and other facilities, at the institution for this purpose. Rates, fees, or rentals collected at one institution shall not be used to discharge bonds or notes issued for or on account of another institution. All bonds or notes issued under the terms of this subchapter shall be exempt from taxation by the state of Iowa and the interest on the bonds or notes is exempt from the state income tax.