California Code, Public Utilities Code - PUC § 29174

The district may provide for redemption of bonds prior to maturity, on such notice and at such time or times and with such redemption provisions, including premiums, as the district may determine, provided that no redemption premium shall be in excess of 6 percent of the principal amount of the bonds to be redeemed.  No bond is subject to call or redemption prior to its fixed maturity date, unless the right to exercise such call and the redemption price are expressly stated on the face of the bond.  When bonds have been validly called for redemption and payment of the principal thereof, and the interest thereon accrued to the date of redemption, together with the redemption premium, if any, shall have been made or provided for, interest thereon shall cease.