Where an order of the director of environmental protection to a person owning and operating a public water system whose rates are regulated by the public utilities commission is final and it is claimed by such person that the revenues derived from the operation of such system is not sufficient to warrant the expense of making the improvements or changes so ordered, an application may be made to the public utilities commission for authority to make and collect additional charges from the water consumers and users of the utility’s service. Upon the filing of such application the commission shall fix a time for the hearing thereof and give notice thereof to the mayor of the municipal corporation and the director. If upon hearing the commission finds that the rates theretofore authorized to be charged will not provide revenue sufficient to operate said system and make a reasonable return upon the investment after such improvements and changes are made, it shall by order authorize the collection of such additional charges and compensation as may be just and reasonable.