Any person, firm, or corporation installing watermains at his, her, or their own expense shall submit plans and specifications for this work to the Department for its approval. After the plans and specifications have been approved by the Department, the work shall be done under the supervision of the Department. All work and testing done must meet city specifications. The provisions of this section shall also apply to any installation of watermains outside the corporate limits of the city where permission has first been granted by the Department to connect those mains to the existing distribution system.