Cal. Pub. Util. Code § 101191

Whenever the board by resolution determines that any record, map, book, or paper which has been in the possession of the district, or any officer or employee thereof, for more than five years is of no further value to the district, the board may authorize its sale, destruction, or other disposition. This section shall not apply to the permanent records of the secretary as provided for in Section 101171, unless such written records are first transferred to microfilm or other miniature or electronic reproduction for permanent preservation.