Any borrower having purchased, constructed, improved, enlarged or repaired any such system, project or combined system pursuant to the provisions of this chapter, (b) issued bonds for any such purpose and (c) failed to provide in the authorizing ordinance for additional bonds for additional construction, improvement, enlargement or repair of such system, project or combined system may, by ordinance, provide for the issuance of additional bonds for further improvement, enlargement, extension or repair of any such system, project or combined system. Such additional bonds, when so issued and negotiated, shall rank junior in standing to the prior issue or issues of bonds for such system, project or combined system and shall so state on the face of the bonds.