A district may issue revenue bonds, not exceeding an aggregate total outstanding of fifty million dollars, to finance construction of projects and incidental facilities authorized by this chapter. Issuance of revenue bonds must be approved by two-thirds of all of the members of the district board. The district shall pledge sufficient revenue from any revenue-producing facility constructed with the aid of revenue bonds for the payment of principal and interest on the bonds     and shall establish rates for the facilities at a sufficient level to provide for the operation of such facilities and for the bond payments. Revenue bonds may not be a general obligation of any political subdivision and may not be secured by property taxes.