California Code, Water Code - WAT § 72072.8

(a) Any service user who fails to pay any tax imposed by this article within 90 days of the date of receipt of notice of the amount of tax due from the service supplier shall pay a penalty of 10 percent of the amount of the unpaid tax.

(b) In addition to the penalty imposed in this section, any service user who fails to pay any tax imposed by this article, shall pay interest at the rate of 6 percent per annum, exclusive of penalties, from the date on which the remittance first became delinquent until paid, and a collection charge of five dollars ($5) for each delinquent account.

(c) The penalties, interest, and collection charges imposed by this section shall not be billed or collected by the service supplier, but shall be determined and collected by the board.