California Code, Public Utilities Code - PUC § 13122

(1) That money may be paid or transferred from any such fund or account in furtherance of the purpose of its establishment, to any other such fund or account established for a like purpose in connection with the same issue of bonds, to such extent as may be required or permitted under the terms of the resolution authorizing that issue;  and

(2) That all money remaining in any such fund or account in excess of the amount required to make provision for the payment in full of the principal of, and interest on, the bonds with respect to which it was established, including premiums, if any, due upon the redemption of any thereof, may be returned and transferred to the revenue fund out of which such reserve fund was established.