Water Code § 51830

If an installment of any assessment has been called to pay the principal, interest, or principal and interest on any outstanding bonds secured by the assessment, and any of the bonds of such maturity have been refunded, or canceled, or not less than 90 percent of the bondholders have entered into and executed a plan for refunding the bonds or for the surrender and cancellation thereof, and by reason of any such facts the payment of the principal of such maturity of such outstanding bonds for which the call, in part or wholly, was levied is not required, the board shall, by resolution, cancel the call to the extent not required.