Cal. Water Code § 26138

Ten years after the issuance of a certificate of sale for the nonpayment of a district assessment or one year after the addition of this section, whichever is the later, it shall be conclusively presumed that redemption was made from the sale, unless prior to such time a deed was issued by the collector pursuant to the certificate of sale and such deed was recorded in the office of the recorder of the county in which the property described in the certificate of sale was located.