Residential Backflow Prevention and Thermal Expansion

The Kennebec Water District requires all customers to install an appropriate backflow prevention device to prevent water from flowing from the home back into the water system. Thus, reducing the possibility of contamination entering the water system. A backflow flow prevention device is a one-way valve that prevents a reversal of water flow in the pipe. At the time of water meter replacement, at residential customers, Kennebec Water District staff can install the backflow prevention device at no labor charge in situations where the interior water pipes are properly aligned. If the water pipes need to be modified, the customer will need to either hire a plumber or modify the plumbing themselves. The cost to the customer for the device is approximately $90 and will be reflected on the next water bill. Residential customers may employ a plumber to install the backflow device or do the work themselves.


Thermal Expansion Control
When heated, water expands. This is referred to as “thermal” expansion. If there is no outlet (a “closed” system) for this expanded water, the water pressure will increase. The Maine Internal Plumbing Code requires that thermal expansion be addressed in plumbing systems to avoid damage to fixtures and appliances. The installation of a backflow device creates a “closed” system that prevents heated water from being forced back into the public distribution system. Thermal expansion, if not controlled can damage or reduce the life of plumbing fixtures and appliances. Thermal expansion may be evident by dripping or spurting from water faucets or intermittent discharge from the pressure relief valve on the hot water heater. Thermal Expansion can easily be controlled by use of a properly sized thermal expansion tank installed on the cold-water supply line. You are encouraged to have a licensed plumber inspect your plumbing system to determine what, if any, steps you should take to meet the Maine Internal Plumbing Code.