11. On or after the effective date of this amendatory Act of the 100th General Assembly, to bill for any utility service, including previously unbilled service, supplied to a residential customer within 12 months, or a non-residential customer within 24 months, after the provision of that service to the customer; however, the water authority may bill for unpaid amounts that were billed to a customer or if the customer was notified that there is an unpaid amount before the effective date of this amendatory Act of the 100th General Assembly for service that was supplied to the customer before January 1, 2016. The time limit of this paragraph shall not apply to previously unbilled service attributed to tampering, theft of service, fraud, or the customer preventing the utility's recorded efforts to obtain an accurate reading of the meter. The trustees shall: (i) label any amount attributed to previously unbilled service as such on the customer's bill and include the beginning and ending dates for the period during which the previously unbilled amount accrued; (ii) issue the makeup billing amount calculated on a prorated basis to reflect the varying rates for previously unbilled service accrued over a period of time when the rates for service have varied; and (iii) provide the customer with the option of a payment arrangement to retire the makeup bill for previously unbilled service by periodic payments, without interest or late fees, over a time equal to the amount of time the billing was delayed. The trustees shall not intentionally delay billing beyond the normal bill cycle. With respect to instruments for the payment of money issued under this Section either before, on, or after the effective date of this amendatory Act of 1989, it is and always has been the intention of the General Assembly (i) that the Omnibus Bond Acts are and always have been supplementary grants of power to issue instruments in accordance with the Omnibus Bond Acts, regardless of any provision of this Act that may appear to be or to have been more restrictive than those Acts, (ii) that the provisions of this Section are not a limitation on the supplementary authority granted by the Omnibus Bond Acts, and (iii) that instruments issued under this Section within the supplementary authority granted by the Omnibus Bond Acts are not invalid because of any provision of this Act that may appear to be or to have been more restrictive than those Acts.