Whenever any area in the district is provided with a sewerage system the governing body of the city in which the area lies may declare the further maintenance or use of cesspools or other local means of sewage disposal to be a public nuisance, and may require all buildings inhabited or used by human beings to be connected with the sewerage system. The board of supervisors may prohibit the use of cesspools or other local means of sewage disposal and declare the same to be a public nuisance in any area in the district which is outside of any incorporated city, and may require all buildings inhabited or used by human beings to be connected with the sewerage system.