(a) The expense of operating and maintaining such systems, including all of the public agency’s obligations to the county authority, its successors or assigns under such contract; and
(b) All of the public agency’s obligations under and in connection with bonds theretofore issued, or which may be issued thereafter and secured by the revenues of such systems. Any such contract may require the use of consulting engineers and financial experts to advise the public agency whether and when such rates and fees are to be adjusted.