65 ILCS 5/11-129-11

All revenue derived from the operation of a water-supply system, improvement or extension constructed or acquired under Section 11-129-9 shall be set aside as collected and deposited in a special fund designated as a municipal water fund for the particular locality. The fund shall be used only for the purpose of paying the cost of operating and maintaining the water-supply system, improvement or extension, providing an adequate depreciation fund, and paying the principal and interest on the bonds issued by the municipality under Section 11-129-9 for the purpose of constructing or acquiring the system, improvement or extension.