Cross Connection/Backflow Devices – Safeguarding Public Drinking Water

When water enters your home from the main water supply line, it should only ever flow in one direction: into your home. But sometimes, due to pressure changes or loss of pressure in the pipes, water can end up flowing backwards and or siphoning back into the main water supply. Backwards running water, known as backflow, happens when water flows in the opposite direction that it’s intended. This occurs anywhere clean water ‘cross-connects’ with any of the following installations: fire protection systems, irrigation systems, and commercial kitchen appliances and the pressure is greater than the pressure at the water main.

Back siphonage is a loss of pressure at the water main creating a vacuum that could pull water mixed with a contaminant not protected with a properly working backflow device.  An imbalance of water pressure can potentially cause unpotable water to backflow into the public water system. Should this occur, it could result in a public health hazard.

Testing for Backflow

Cross-connection devices/ backflow preventers are used to prevent this opposite flow of potentially contaminated water from reaching the main water supply line. Lynnfield Water District performs cross-connection tests semiannually in the spring and fall to ensure devices are working properly.  These devices are tested semiannually to ensure they are working properly.

How do I know if I have a backflow device or if I need one?

All commercial and industrial properties along with irrigation meters are required to have a backflow prevention assembly. Most residential properties are not required to have one.

When a plumbing fixture is connected to drinking water supply, a potential cross-connection exists there. Some commercial and residential examples of this are:

    • Swimming pools and spas
    • Wash basins and service sinks
    • Irrigation or lawn sprinkler systems
    • Food and beverage processing equipment
    • Chemical feed equipment
    • Laboratory equipment
    • Fire sprinkler systems
    • Attachment to hose to apply weed killer or fertilizer or to flush antifreeze
Lynnfield Water District follows the regulations of the EPA to protect public drinking water when implementing its cross-connection testing program. For more information on cross-connections/backflow, please visit MWRA – About Cross-Connections or United States Environmental Protection Agency – Cross-Connection PDF

Reduced Pressure Zone Backflow Preventer (Source W. W. Grainger)