Whenever such governing body deems it expedient to issue refunding bonds under the provisions of this part 7 and the net interest cost and the net effective interest rate of the proposed issue of refunding bonds does not exceed the net interest cost and net effective interest rate of the issue of bonds to be refunded, such refunding bonds may be issued without the submission of the question of issuing such refunding bonds to a vote of the qualified electors of the county. The issuance of bonds under this part 7 for the purpose of refunding bonds which were originally issued to supply water to the county shall not require approval ofsuch electors.