65 ILCS 5/11-136-1
Any 2 or more municipalities, except cities of 500,000 or more inhabitants, may acquire either by purchase or construction a waterworks system or sources of supply of water or sewer systems, or any combination thereof, and may operate jointly a waterworks system or sources of supply of water or sewer systems, or any combination thereof, and improve and extend the same, as provided in this Division 136. The corporate authorities of such municipalities desiring to avail themselves of the provisions of this Division 136 shall adopt a resolution or ordinance determining and electing to acquire and operate jointly a waterworks system or sources of supply of water or sewer systems, or any combination thereof, as the case may be. This Division 136 shall not be construed as limiting, amending or repealing any other laws with respect to joint acquisition and operation of a waterworks system or sources of supply of water or sewer systems, or any combination thereof, but shall be considered as an additional grant of power for the purposes herein set out.
65 ILCS 5/11-136-1