California Code, Public Utilities Code - PUC § 30705

The district may also refund any indebtedness as provided in this part or in any other applicable law.  The board may provide for the issuance, sale or exchange of refunding bonds to redeem or retire any bonds issued by the district upon the terms, at the times and in the manner which it determines.  Refunding bonds may be issued in a principal amount sufficient to pay all or any part of the principal of any bonds outstanding, the interest thereon and the premiums, if any, due upon call and redemption thereof prior to maturity and all expenses of such refunding.  The provisions of this part for issuance and sale of any bonds apply to the issuance and sale of such refunding bonds;  except that (i) the issuance of refunding bonds shall be approved by 60 percent of the votes cast by the qualified electors of the district voting at an election called and held for that purpose except that an election is not required if the refunding is by the same type of bonds and payable from the same sources, and (ii) when refunding bonds are to be exchanged for any bonds outstanding the methods of exchange shall be as determined by the board.