(b) Commencing January 1, 1982, if all or part of the bill is not paid, and the ratepayer states the reason for the nonpayment of a component or components of the bill, the local agency may discontinue only that service related to the component of the bill which is not paid, except that if all or part of the component of the bill related to sewer service is not paid the water service may also be discontinued. However, if any of the services for which the bill was rendered were financed pursuant to revenue bonds issued prior to January 1, 1982, and which have not been retired, the local agency may apply the provisions of subdivision (a).