Bonds issued under the provisions of this chapter shall be limited obligations of the district payable solely from the sources pledged for the payment thereof. All such bonds shall contain a statement on their face substantially to the effect that neither the full faith and credit of the state nor the full faith and credit of any governmental unit of the state are pledged to the payment of the principal of or the interest on such bonds. Except as provided in a contribution agreement, the issuance of bonds under the provisions of this chapter shall not directly, indirectly or contingently obligate the state or any governmental unit of the state to levy any taxes or to make any appropriation for their payment arising out of contracts authorized under this chapter.