65 ILCS 5/11-133-3
Whenever certificates of indebtedness are issued pursuant to this Division 133, the entire revenue received from the operation of the waterworks system shall be deposited in a separate fund, designated as the water fund of the municipality of ..... This fund shall be used only in paying (1) the cost of maintenance and operation of the waterworks system, (2) obligations of the municipality theretofore issued that are payable by their terms from this revenue, whether in the form of certificates, bonds, or otherwise, and (3) certificates issued pursuant to this Division 133.
Rates charged for water shall be sufficient to pay the cost of maintenance and operation and to pay the principal of and interest upon all of the specified certificates and bonds. These rates shall not be reduced while any of these certificates or bonds are unpaid.
65 ILCS 5/11-133-3