§ 56. Issue of licenses to connect with sewers and water mains restricted. The commissioner of public works of any city, or the officer or officers acting in a like capacity in any of the cities of this state, and having charge of the sewers and water mains therein, shall not issue a license to any one to connect with the sewers or with the water mains of such cities, unless such person has obtained and shall produce a certificate of competency from the examining board of such city.