MEP Culture Blog

Backflow Prevention in Commercial Buildings

Thursday, December 15, 2011

One of the most precious natural resources for human survival is fresh water. Here in the United States, it is assumed that cities, municipalities, counties and special districts within our governing agencies will provide clean fresh water to the citizens residing in these places. We consume fresh water for several uses such as drinking, washing and commercial or industrial purposes. It is our duty as educated citizens, neighbors and engineers to protect this valuable resource as much as possible. One way to protect our fresh water system is to provide backflow prevention devices in our commercial and residential buildings.

A backflow condition in the domestic water system is the unwanted reversal of the flow of water or mixtures of water and other unwanted substances from any source.  Sources would include waste water, industrial waste water, or any substance harmful to the domestic water system.

There are several types of backflow conditions that can occur: cross connection, backpressure and backsiphonage. The following definitions are from the American Water Works Association (AWWA).

Cross connection: any unprotected actual or potential connection or structural arrangement between a public or consumer's potable water system and any other source or system through which it is possible to introduce into any part of the potable system any used water, industrial fluid, gas, or substance other than the intended potable water with which the system is supplied.

Backsiphonage: backflow caused by negative or reduced pressure in the supply piping

Backpressure: A potable system connected to a non-potable supply operating under higher pressure by means of a pump, boiler, elevation difference, air or steam pressure has a high risk that non-potable water may be forced into the potable system whenever these interconnections are not properly protected.

The Safe Drinking Water Act, signed into law by President Ford, placed more emphasis on the responsibility for drinking water protection. Backflow prevention devices protect the public safety by preventing potable water contamination.

There are several backflow manufacturer’s available in the industry. A few are listed below:

Sizes of backflow preventers range from 24” long for a 1” to 2” device, and 43” for a 2-1/2” and

3” device and 47” for a 4” device. The size of the backflow preventer shall match the pipe size diameter of the water service coming into the building.


Today’s building codes, plumbing codes and city ordinances require the installation of backflow prevention device to be installed on domestic water service piping and fire protection piping in all new commercial buildings. It is also required to retrofit such building water services with a backflow prevention device in existing buildings.

Backflow preventers are installed in plumbing and fire protection systems to protect the city water supply or they can be installed to protect the water supply within a building. There are numerous types of backflow prevention devises available and it’s the plumbing engineer’s responsibility to determine the severity of the possible backflow condition and design a device that will protect the public drinking water system in the best possible way.