The provisions of this part requiring any city or town acquiring a waterworks or sewerage system to create a board of waterworks or sewerage commissioners, defining their duties, qualifications, method of appointment or election, term of office, compensation, time of meetings, organization, removal from office and powers, shall not apply to any city or town having in existence on April 11, 1933, a department, board or commission, invested with similar duties and powers, and, in its discretion, any such city or town may substitute for the board of waterworks or sewerage commissioners provided for in this part such department, board or commission as is in existence on April 11, 1933, which shall be clothed with all powers and duties given to the board of waterworks or sewerage commissioners by this part, but shall be required to qualify by giving bond or taking oath as provided in this part.