A joint system may incur debt for any of its purposes and may issue bonds pledging to the payment as to both principal and interest the revenues, or any portion, derived or to be derived from all or any of its projects and any additions and betterments or extensions or contributions or advances from its members or other sources of funds available to it. A joint system may not undertake a project required to be financed, in whole or in part, with the proceeds of bonds without the approval of the governing bodies of each member which is obligated or to be obligated under any contract for the payment of amounts to be pledged as security therefore and a favorable vote of two-thirds of all commissioners. A joint system formed only for the purpose of creating a financing pool may issue notes in anticipation of the issuance of bonds by its members to the government.