Mich. Comp. Laws § 324.4712
If the governing body of a district formed under this part acquires, extends, improves, or operates a sewage disposal system or water supply system or provides for the sale and purchase of sewage disposal service or water supply service from an existing system or systems and executes contracts that may be necessary, the authority may, pursuant to any contract entered into under section 4709, issue self-liquidating revenue bonds in accordance with the revenue bond act of 1933, Act No. 94 of the Public Acts of 1933, being sections 141.101 to 141.140 of the Michigan Compiled Laws, or any other act providing for the issuance of revenue bonds. However, these bonds are payable solely from the revenues of the sewage disposal system or the water supply system. The charges specified in any contract are subject to increase by the district at any time if necessary to provide funds to meet its obligations and any contract authorized by this part is for a period of not more than 40 years. The legislative body of any municipality that enters into a contract with the district may raise by taxes or pay from its general funds any money required to be paid under the terms of the contract to obtain maps, plans, designs, specifications, and cost estimates of the proposed sewage disposal system or water supply system.
MCL 324.4712