Extension of mains; contracts; water rate surcharges or cash connection charges

The board of commissioners in cities of the first class before making any water main extension may require contracts, bonds or other evidence of future use insuring to such city a reasonable additional income therefrom. Such cities may make a water rate surcharge to water consumers, within or without such city, served by any water line extension hereafter made by such city or such cities may make a cash connection charge to property owners based on a linear foot cost of such water line extension to reimburse the city for the cost of such extension: Provided, Such surcharge, if made, shall be for a specified period of years, and shall be calculated to return to such city no more than the cost of such extension, plus reasonable interest charge thereon.