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Backflow Prevention

What is Back-flow?
Back-flowis an unintended flow of water running in the opposite direction in the plumbing system.  Normally water flows from the distribution system through the customer’s meter and into the facility. Backflow occurs when hydraulic conditions within the system change as a result of a sudden reduction in water system’s pressure. Backflow can also happen when the customer’s water pressure increases above that of local water distribution system.

The primary causes of back-flow are back-pressure and back-siphonage.

1 –Back-pressure incidents can occur when the pressure on your system exceeds the pressure in the water distribution system. Examples include a car wash that pumps and re-circulates soapy water, or a manufacturing plant that uses substantial water pressure for production.  Back-pressure can result from an increase in downstream pressure, a reduction in the potable water supply pressure, or a combination of both.

2- Backsiphonage is the reversal of the normal flow of water when there is a low or negative pressure on the public drinking water distribution system. It may be caused on the supply side of the system when there is an increased water usage during fire fighting, a break on a water main, or when a motorist hits a fire hydrant and causes damage.

backflow, cross-connection

Why is back-flow prevention important?

Plumbing problems like a water main bursts, pipes freeze or an unexpectedly high demand on the water system can also create a suction effect, possibly drawing contaminated water into the drinking water system. For this reason, back-flow or cross-connection can be a serious health risk. It allows contaminants such as fertilizers, pesticides or animal residues to flow back into potable water supply system. Connections between the water supply and a source of contamination are called cross-connections.  There are documented cases of cross connection/back-flow incidents that have contaminated potable water supplies, and, in some cases, caused illnesses and deaths.


The State of Tennessee requires mandatory backflow preventers on all commercial, industrial and most residential water systems, specially where high health hazard are normally found, such as:

  • Car washes
  • Food and beverage processing centers
  • Hospitals, mortuaries, clinics
  • Laboratories
  • Metal plating and chemical plants
  • Petroleum processing and storage plants
  • Piers and docks Sewage treatment plants.

Back-flow Preventers are mechanical plumbing devices installed in a plumbing system to prevent water from flowing backwards and becoming contaminated.   A certified assembly tester must inspect and test all back-flow prevention assemblies at the time they are installed and annually thereafter.

Don Wood Plumbing is a Certified Nashville Back-flow-Prevention Tester  and expert in the installation, repair, maintenance and service of back-flow preventers.  We also have experienced back-flow technicians on staff ready to answer questions and assist you regarding repairs and parts and testing. Call Don Wood Plumbing at (615) 366-9663 to schedule service today!