Backflow Prevention

Small gray valveThe water that runs through the pipes of the City of McDonough Water Distribution system is meant to run in one direction. When water attempts to run in the opposite direction in the system, it is called backflow. There are two conditions that can cause backflow. It may occur due to either backsiphonage or backpressure in the water system.

  • Backsiphonage can occur when a water main or plumbing system in a building loses water pressure, thus creating a reduced pressure in the water supply piping. This reduced to flow opposite of the normal direction of flow. Such pressure differences can cause siphoning of non-potable water and other liquids back into the potable water lines.
  • Backpressure occurs when water pressure in a building or fixture becomes greater than the water pressure in the water supply piping. This condition can force non-potable water or other fluids back into the potable water system.

Backflow can take place within any water distribution system whether it is private or public. Backflow can be one of the greatest threats to the safety and integrity of a local water system. For that reason, The City of McDonough has implemented a Backflow Prevention Program to ensure the prevention of potentially hazardous cross-connections (any actual or potential connection between the public water supply and a source of contamination or pollution) to the public water system.

Blackflow prevention deviceCity of McDonough requires all commercial and/or industrial facilities to have an approved backflow prevention device installed. All homes constructed after 2001 should also have backflow prevention devices. Additionally, whenever City of McDonough rehabs older water lines in a subdivision, backflow prevention devices are installed.

While protecting a public drinking water system from potential backflow, these devices also seal water off inside a customer's home. As a result, a backflow prevention device could create higher pressure on an existing plumbing system (both on the hot water and cold water side).

For some homeowners, a spike in pressure also could set off the relief valve on hot water heaters or cause other damage to the plumbing system and/or the house. Thus, customers should check to make sure pressure relief or thermal expansion devices are installed and operating properly on or within their plumbing systems.

Larger backflow deviceAs a result of a change in the plumbing code in 2001, all homes built since that time are required to have such thermal expansion devices included in their construction. However, homes built prior to 2001 may not have these capabilities inside the house. Customers should consult a certified plumber if they have any doubts about their plumbing's condition. 

The HCWSA will not be responsible for any plumbing problems that may arise as a result of non-existing or improperly installed thermal expansion or pressure relief equipment. Commercial and industrial facilities are required to have their backflow prevention devices tested periodically by someone who is certified. 

For further information contact City Hall 770-957-3915.