Any sewer district which may be organized under sections 249.010 to 249.420 is hereby authorized to fund or refund any part or all of its bonded indebtedness, including bonded indebtedness incurred on behalf of any subdistrict, in the same manner as is now provided by section 108.140; provided, however, that the interest on and principal of any refunding bonds which may be issued shall be paid only out of funds provided in the same manner as is provided in sections 249.010 to 249.420 for the payment of the interest on and principal of the bonds so refunded.