Cal. Water Code § 9046

If it appears to the trustees of any such district that any such warrants owned by it will be paid from any assessment thereafter to be levied, and in their opinion 85 per cent, or more, of the moneys necessary to pay the warrants will be raised by an assessment on the lands within the district, the trustees may return the warrants to the board for cancellation and the warrants shall be canceled by the board and thereafter are inoperative and of no effect.