Water Code § 71671
ARTICLE 2. Sewage, Waste, and Storm Water Disposal
The revenues from the rates and charges for services and facilities furnished pursuant to this article may be used for the following purposes:
(a) To pay the operating and maintenance expenses of the facilities.
(b) To provide a reasonable surplus for improvements, extensions, and enlargements.
(c) To pay the interest on any bonded debt for the facilities.
(d) To provide a sinking or other fund for the payment of the principal of such bonded debt as it becomes due.