When the expense in connection with the waterworks system is to be raised by general taxation, no contract for construction, purchase, lease, or maintenance which shall stipulate for an annual payment greater than an annual levy of five mills on each dollar of the assessed valuation of the municipality shall be authorized until such contract shall first have been submitted to a vote of the voters of such municipality at a general or special election and ratified by a majority of those voting at such election.
(SDCL § 9-47-4)