(a) Every waterworks corporation shall establish procedures whereby any complaint filed with such corporation by any customer thereof in regard to any bill for service rendered or any deposit required will be promptly investigated in an appropriate and fair manner, with the result of such investigation being promptly reported to the complaining customer. Such procedures shall allow the acceptance and processing of complaints submitted in simple manner and form. Regardless of whether a notice of discontinuance has previously been sent, the utility's procedures shall provide that pending the utility's investigation it shall not discontinue service or issue a notice of discontinuance; provided, however, the consumer may be required to pay the undisputed portion of a disputed bill or deposit to prevent discontinuance or the issuance of a notice of discontinuance.

(b) If, after the completion of such an investigation, the utility determines that the disputed service has been rendered, or that the disputed charge or deposit is proper, in whole or in part, the utility may require the full bill or deposit or the appropriate portion thereof to be paid; in such event, appropriate notice of the determination shall be given to the customer, and where notice of discontinuance of service has previously been sent, or is served with the determination, such notice shall include a statement advising the customer of the availability of the commission's complaint handling procedures. The utility's procedures may provide for discontinuance of service if the customer fails to pay such required amount after receipt of proper notice, provided that a customer's service will not be discontinued until at least five days after notice of the utility's determination, where personal service is made upon the person supplied, or at least eight days after mailing of such a notice; and provided further that a customer's service shall not be discontinued, nor shall a notice of discontinuance be issued, if a complaint regarding a bill or deposit has been made to the commission and the customer pays the undisputed portion of any bill for service, including bills for current usage, during the commission's investigation of such complaint, unless the commission shall otherwise order.

(c) The utility's procedures shall provide that, where the complaint procedures of the commission have been invoked and it is determined that the disputed service has been rendered, or that the disputed charge or deposit is proper, in whole or in part, a customer's service will not be discontinued for failure to pay the amount found appropriate until at least 15 days after notice of the commission's determination.

(d) The procedures required to be established under this section shall be filed with the commission for review. The commission shall be advised of any substantial changes in such procedures 30 days prior to their proposed implementation to permit commission review.