California Code, Public Utilities Code - PUC § 33005

Special benefit assessments for the payment of the principal of, and interest on, bonds issued for a benefit district shall be levied in the benefit district at rates which are sufficient in the aggregate, together with revenues already collected and available therefor, to pay the principal of, and interest on, all bonds of the district issued for the benefit district. Other revenues of the district shall be used for the payment of the principal of, and interest on, the bonds only to the extent set forth in any agreement of the district for the benefit of bondholders.

Special benefit assessments in the benefit district and zones, if any, therein shall be calculated to reflect, as accurately as possible, the benefit received by the property assessed in the benefit district or zones, if any, therein as a result of the project to be financed thereby.