What is the best method to avoid contamination of a main when installing a new service connection?

The best method to avoid contamination of a main when installing a new service connection is to leave the main pressurized and install the fitting by wet tap. This approach ensures that the main remains under pressure during the installation process, which helps to prevent any external contaminants from entering the water distribution system.

When pressure is maintained, there is a continuous flow that pushes any potential pollutants or contaminants away from the connection point, greatly reducing the risk of introducing harmful substances into the main. The wet tap method involves making the connection while the water is still flowing, allowing for a more controlled and sanitary installation.

Other methods, such as draining the main or using a dry connection method, can create opportunities for contamination because they either reduce the pressure, allowing backflow of contaminants, or do not provide a barrier against external pollutants during the installation process. Installing a valve before the fitting does create a point of isolation, but it does not inherently prevent contamination during the actual installation of the service connection. Therefore, maintaining pressure and using a wet tap is the most effective method for safeguarding the integrity of the water supply.