What is backflow?

Backflow is the reversal of the intended direction of flow of water or mixtures of water and other liquids, gases or other substances into the distribution pipes of a potable water system from any source. Backflow prevention and cross connection control are regulated in Tennessee under section 68-221-701 through 68-221-720 of the Tennessee Code Annotated.

    What causes backflow?
  • Backpressure, a pressure in the downstream piping that is higher than the supply pressure. Common examples that may cause backpressure in Tennessee:
    • Pumping systems without backflow prevention assemblies, including fire pump systems and booster pump systems.
    • Potable water connections to boilers and other pressure systems without backflow prevention assemblies.
    • Connections with another piping system that may, at times, have a higher pressure.
    • Water stored in tanks or plumbing systems that by virtue of elevation would create head sufficient to cause backflow if pressure were lowered on the public system.
  • Backsiphonage, a negative or sub-atmospheric pressure in the supply piping. Common examples that may cause backsiphonage in Tennessee:
    • Undersized piping.
    • High velocity flow (when combined with undersized piping causes the aspirator effect).
    • Line repair or break at a lower elevation.
    • Lowered pressure in the water main due to a high water withdrawal rate, such as fire fighting, line break or water main flushing.
    • Reduced supply main pressure on the suction side of a booster pump or fire suppression system pump.

What are possible affects from backflow conditions?
Without protection from the correct backflow prevention device, any of the above mentioned examples could contaminate the public water supply and put public health at risk.

Who is responsible for protecting the public water system against contamination through cross connection and backflow prevention in Tennessee?
The water customer is responsible for the installation, operation and maintenance of backflow prevention assemblies as may be necessary for the protection of the community water system. In Tennessee, many water purveyors consider their responsibility ending at the point of delivery to the customer’s private water lines. T.C.A. 68-221-701 through 68-221-720 and the Federal Safe Drinking Water Act hold the water purveyor responsible for the quality of water delivered.

If you have any further questions regarding backflow prevention and cross connection management, the following links may be of help:

www.tnbackflow.com
www.abpa.org
water.epa.gov/infrastructure/drinkingwater/pws/crossconnectioncontrol/
crossconnectioncontrol_manual.cfm