The governing authority of the district by resolution may authorize the issuance of refunding bonds, and such refunding bonds may be either sold and the proceeds applied to or deposited in escrow for the retirement of outstanding bonds or they may be delivered in exchange for the outstanding bonds.  The total of principal and interest to be paid upon any such refunding bonds shall not exceed the total of the principal amount of the bonds to be refunded, the premium (if any) payable upon their redemption and the interest which would have been paid upon such bonds were they not to be refunded.

Acts 1969, No. 43, §4.