. . . "Such The bonds may be issued as provided in s. 66.066 66.0621 (2) and shall pledge income from hydrant rentals and all sewer and water charges and may contain any covenants authorized by law, except if bonds are issued under this section to refund floating indebtedness, the bonds shall be are subject to the prior lien and claim of all bonds issued to refund revenue bonds issued prior to the refund" .