Cal. Water Code § 60405

If, by the certificate of the secretary of the district, the petition is found to be insufficient, he shall also certify to the number of voters required to make such petition sufficient, and it may be amended by filing a supplemental petition or petitions within ten (10) days of the date of such certificate. The secretary of the district shall, within ten (10) days after the filing of such supplemental petition or petitions, make like examination of the same and certify to the result of such examination as hereinbefore provided.