At any time after the appointment of the commission any municipality in which water is supplied by the waterworks which it is proposed to acquire, or which may have been acquired as provided in sections 40:62-108 to 40:62-150 of this title may be permitted to join with the municipalities making or joining in the application for the appointment of the commission, or owning the waterworks, on such terms and conditions as may be agreed on, provided that municipalities containing at least two-thirds of the population of all the municipalities seeking to acquire or owning such waterworks shall agree to permit such other municipality to join.