It shall be unlawful for any person to do any plumbing in any city or village, or within the area of extraterritorial zoning jurisdiction of cities of the metropolitan class, which has established a plumbing board unless the person holds a proper license. It shall be unlawful for any person to make any connection to water mains extended from within and beyond the extraterritorial zoning jurisdiction of a city of the metropolitan class which has established a plumbing board, unless the person complies with the applicable plumbing codes of the city of the metropolitan class and holds a proper license as required by such city. The requirements of this section shall not apply to employees of the water utility of such city or village acting within the scope of their employment.