Cal. Pub. Util. Code § 13151.5

The board may provide for such bonds being redeemable, either at the option of the district, or in the operation of any sinking fund provided for the issue, at such price or prices and in such manner as the board may determine, whether or not involving the payment of a premium upon such redemption; provided, that no bond shall be subject to redemption unless such bond at the time of its issue states on its face that it is redeemable at the option of the district or by the operation of a sinking fund for bonds of that issue, as the case may be.