For the purpose of owning, operating, constructing, maintaining, and equipping a sewerage disposal system and plant or plants as authorized by the County Industrial Sewer Construction Act or improving or extending an existing system, a county may make a special levy known as the sewer tax levy not to exceed three and five-tenths cents on each one hundred dollars upon the actual value of all the taxable property within any such county subject to section 77-3443. Any levy exceeding such amount for the purposes of such act shall be submitted for approval to the registered voters of the county at a general election or special election called for such purpose. The proceeds of such levy shall be used only for the purposes enumerated in this section and for no other purpose.