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About Backflow Prevention and Cross Connection Control

What is Backflow?

Backflow is the reversal of water’s normal direction of flow. When water passes through a water meter into a customer’s home or business it should not flow back into the County water main. If it does, the condition is referred to as “backflow.” Backflow prevention is keeping the unintentional reversal of water flow from occurring.

backflow device

How Does Backflow Take Place?

There are two types of backflow conditions back pressure and back-siphonage.  The first is a back pressure that occurs when the pressure in the consumer's line is greater than the pressure in the public water system's supply line. Examples, when using well water, gray water, and rainwater pump to irrigate and being dually connected to the public water supply: pumping at a higher pressure creates backflow pressure, possibly pumping into the public supply.  The second is a back siphonage. This occurs when the pressure in the public water system drops and backflow occurs, causing water to flow backward in a reverse direction or back siphonage condition.  The backflow device is designed to prevent and protect our water system from both of these conditions.

Prevention of backflow is critical to a water utility because of the potential for contamination of the water system. In the absence of backflow prevention devices and assemblies, reversed water can be drawn back into the distribution system and it may be accessed by other users.

If a backflow incident results from industrial customers who may handle hazardous materials, the public system can become contaminated.

backflow device
backflow device

Cobb Water is serious about our mission to protect customers, water resources, and the environment. Our objective is to monitor assemblies and install devices which will prevent the water supply from becoming contaminated, even unintentionally. It is essential for the community to be aware of the harmful impact of backflow. Through education, we can reduce and prevent the occurrence of backflow.  Working with the public as a team, the Cobb County Water System will provide direction to medium and high-risk Cobb businesses on the installation of appropriate backflow prevention devices.

Backflow Prevention FAQs

What is backflow prevention?

It is the prevention of reverse flow in a water system from the normal or intended direction.

What is Thermal Expansion?

Thermal expansion refers to the characteristic of water to expand when it is heated. Unlike air, which can be compressed, water grows in volume and must be accommodated.

Are there any building codes with requirements for resolving thermal expansion problems?

Yes. Section 607.3.2 of the Standard Plumbing Code states that if a system with a water heater has a backflow prevention device installed and as a result thermal expansion causes an increase in pressure, a device must be fitted to limit the pressure to 80 pounds per square inch (psi) or less.

Why is Thermal Expansion occurring?

In a water heater, thermal expansion can create more pressure than the system can handle. When unchecked, this pressure can result in expensive leaks, as well as damage to the water heater, pipes, or other fixtures.

Where can I get a thermal expansion solution?

Thermal expansion solutions are available at hardware stores or your local plumbing vendors.

When is a Thermal Expansion device necessary?

Thermal expansion is necessary when any of the following occurs:

  • A recent water meter replacement
  • A hot water heater replacement
  • The construction of a new home
  • When a backflow preventer is installed on the water

Please contact below for more information if you have further questions regarding the thermal expansion requirements and alternatives.

Roger Boss
☎  770.528.3343

How do I resolve Thermal Expansion?

Thermal expansion can be solved by installing an expansion tank to your system adjacent to your water heater. This tank will accept overflow from your water heater, alleviating the pressure building up in the heating tank. Expansion tanks are inexpensive and the most conservation-friendly solution. There are also several other relief solutions available. Talk to your local plumbing or hardware vendor regarding these alternatives.

I have a Temperature and Pressure Relief (T&P) valve, is that sufficient?

No. A T&P valve is not a thermal expansion device, because the constant dripping of water from the valve can result in a mineral deposit that can create a blockage, causing the T&P valve to become ineffective. Plumbing standards and codes require that thermal expansion be properly addressed.

What can cause something like this to happen?

Backflow and/or back-siphonage can occur in a water system by a drop in supply pressure due to heavy demand or use such as firefighting, or by repairs or breaks in the supply pipe, etc.