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.