65 ILCS 5/9-2-134
The entire proceeds arising from the operation of such waterworks system shall be paid into the municipal treasury and shall be kept in a separate fund to be known as the "waterworks fund." After the payment therefrom of the necessary running and operating expenses of the waterworks system, the balance from time to time shall be credited by the municipal treasurer upon the assessment levied against the municipality for public benefits and the respective installments thereof, and shall be applied toward the payment of the cost of the waterworks system in the manner provided by this Division 2. Until the bonds so issued to pay the cost of the construction of the waterworks system and the interest thereon have been fully paid, the municipal treasurer shall not pay any warrant drawn on the "waterworks fund" for any other purpose except for the payment of the necessary operating expenses of the waterworks system.
In case such a waterworks system is used and operated to supply water for any existing distributing system, the entire proceeds derived from the operation of the waterworks system and the distributing system so supplied with water shall be apportioned and divided in proportion to the original cost of the distributing system, and the cost of the waterworks system. These costs shall be determined by the municipal clerk. The portion of such income that is so determined to arise from the operation of the waterworks system shall be paid to the municipal treasurer and placed in the "waterworks fund" and used only in the manner specified in this section. The provision of this section shall not apply to any city having a population of 500,000 or more.
65 ILCS 5/9-2-134