N.D. Cent. Code § 43-18-10

No person, firm, corporation, or limited liability company shall engage in the business of installing plumbing and shall not install plumbing in connection with the dealing in and selling of plumbing materials and supplies in any location of this state having a public system of waterworks or sewerage, unless at all times a registered and licensed master plumber, who is responsible for the proper installation thereof, is in charge of such work. In cities of less than one thousand population and in all rural areas, a licensed journeyman plumber may engage in the business of installing plumbing.