California Code, Government Code - GOV § 54348

The local agency may provide for a basic penalty for nonpayment of the charges within the time and in the manner prescribed by it.  Said basic penalty shall not be more than 10 percent of each month's charges for the first month delinquent.  In addition to the basic penalty it may provide for a penalty of not exceeding one-half of 1 percent per month for nonpayment of the charges and basic penalty.  On the first day of the calendar month following the date of payment specified in the bill the charge shall become delinquent if the bill or that portion thereof which is not in bona fide dispute remains unpaid.  It may provide for collection of the penalties herein provided for.