Backflow is a plumbing problem that can allow contaminated or non-potable water to flow backward into a clean water supply. Because this can create a serious cross-connection and water-quality risk, homes and businesses may need properly selected and maintained backflow preventer devices to protect their potable water systems.
Modern backflow prevention systems are designed to stop unwanted reverse flow and help keep contaminated water from entering drinking-water lines. The type of backflow preventer required depends on the property’s plumbing configuration, the potential source of contamination, local plumbing codes, and the requirements of the water utility or authority having jurisdiction.
What Is Backflow?
Backflow occurs when water flows in the opposite direction from its intended path. Under normal conditions, potable water moves from the public water supply toward a property and its plumbing fixtures.
A change in pressure or another plumbing condition can cause water from a connected system to move backward. If that water has been exposed to chemicals, fertilizers, wastewater, irrigation water, or other contaminants, it can potentially enter the potable water system.
Backflow is generally associated with two conditions: backsiphonage and backpressure.
What Is Backsiphonage?
Backsiphonage can occur when the pressure in the potable water supply drops below the pressure in a connected system. This can create a siphoning effect that pulls water backward through a cross-connection.
A water-main break, firefighting activity, maintenance, or other sudden changes in water pressure can contribute to conditions where backsiphonage becomes possible.
What Is Backpressure?
Backpressure occurs when pressure in a connected plumbing system becomes greater than the pressure in the potable water supply.
For example, elevated pressure from pumps, boilers, or other equipment can potentially force water backward toward the potable supply if appropriate backflow protection is not installed.
What Is a Backflow Preventer?
A backflow preventer is a plumbing device or assembly designed to prevent unwanted reverse flow into a potable water supply.
Backflow preventers use valves, pressure differences, air gaps, or other protective methods to separate potable water from potentially contaminated sources. Different devices are designed for different levels and types of backflow hazards.
A backflow preventer is not simply a universal valve that can be installed anywhere. The correct protection depends on the plumbing application and the level of hazard involved.
How Do Backflow Preventer Devices Work?
The operating principle depends on the type of backflow prevention assembly.
In general, the device allows water to travel in the intended direction while providing protection if reverse flow conditions develop.
Some systems use check valves to restrict reverse flow. Others use pressure zones, relief valves, or an air gap to provide additional protection.
If a backflow prevention assembly is installed incorrectly, damaged, or not maintained, it may not provide the protection the plumbing system requires.
Types of Backflow Preventers
Different plumbing applications require different forms of backflow protection. Common types include:
Atmospheric Vacuum Breaker
An atmospheric vacuum breaker uses an air inlet to help protect against backsiphonage. These devices are commonly associated with certain irrigation and plumbing applications.
They are not suitable for every backflow condition, so proper application is important.
Pressure Vacuum Breaker
A pressure vacuum breaker, or PVB, is designed to protect against backsiphonage while operating under continuous pressure when installed according to its approved application.
PVB assemblies are commonly used in irrigation systems and other applications where the appropriate level of protection is required.
Double Check Valve Assembly
A double check valve assembly, or DCVA, uses two independently acting check valves to help prevent reverse flow.
These assemblies are commonly used in applications where the potential hazard and local requirements permit this level of protection.
Reduced Pressure Principle Assembly
A reduced pressure principle assembly, often called an RP or RPZ assembly, provides a higher level of backflow protection for certain higher-hazard applications.
These assemblies use two check valves and a relief valve to help protect the potable water supply if pressure conditions change.
The exact backflow protection required should be determined by a qualified professional based on the property’s plumbing system, potential contamination source, and applicable regulations.
Where Are Backflow Preventers Used?
Backflow prevention may be required or recommended in many residential, commercial, and industrial applications.
Examples can include:
- Irrigation and sprinkler systems
- Hose bibs and outdoor faucets
- Swimming pools and related equipment
- Commercial plumbing systems
- Boilers and heating systems
- Fire protection systems
- Equipment connected to potable water
- Properties with chemical or process-water connections
- Certain commercial and industrial facilities
The requirements vary depending on the application and local regulations.
Why Is Backflow Prevention Important?
The primary purpose of backflow prevention is to protect potable water from potential contamination.
A plumbing system can have multiple connections where potable water interacts with other systems or substances. Without appropriate protection, a change in pressure could create an opportunity for contaminated water to move in the wrong direction.
Proper backflow prevention can help:
- Protect potable water supplies
- Reduce cross-connection risks
- Protect occupants and customers
- Meet applicable plumbing requirements
- Protect irrigation and other connected systems
- Reduce the risk associated with contaminated water entering potable plumbing
Do Homes Need Backflow Preventers?
Not every home requires the same type of backflow prevention device.
Residential properties may have backflow risks associated with irrigation systems, hose connections, pools, boilers, or other plumbing equipment. Local water providers and plumbing authorities may also have specific requirements.
A professional evaluation can determine whether backflow protection is necessary and which type of device is appropriate for a particular installation.
Backflow Prevention for Irrigation Systems
Irrigation systems are a common area where backflow protection can be important because irrigation water can come into contact with fertilizers, pesticides, soil, and other substances.
A properly selected backflow prevention assembly helps separate the irrigation system from the potable water supply.
If you are installing or modifying an irrigation system, check local requirements before selecting a backflow prevention device. Some jurisdictions require specific assemblies, testing, installation methods, or annual certification.
Backflow Testing and Inspection
Installing a backflow preventer is only part of protecting a plumbing system. Some backflow prevention assemblies require periodic inspection and testing to verify that the components continue to operate properly.
Testing requirements vary by device type, property type, water provider, and local regulations.
A certified or otherwise qualified backflow tester may be required to perform testing and submit documentation to the appropriate authority.
Why Does Backflow Testing Matter?
Regular testing can help identify problems such as:
- Failed check valves
- Pressure problems
- Damaged components
- Improper operation
- Debris or mineral buildup
- Installation issues
If a required backflow assembly fails testing, repairs or replacement may be necessary before the system can be considered compliant.
How Often Should a Backflow Preventer Be Tested?
There is no single testing schedule that applies to every property.
Testing frequency depends on the type of assembly, its application, local plumbing regulations, and requirements established by the local water authority.
Some commercial and irrigation systems may require annual testing, while other systems may have different requirements.
Property owners should follow the schedule established by the applicable water utility or regulatory authority rather than assuming that the same schedule applies everywhere.
Signs a Backflow Preventer May Need Attention
Backflow prevention equipment should be professionally evaluated if you notice:
- Visible leakage around the assembly
- Damaged or corroded components
- Unusual pressure changes
- A failed backflow test
- Problems with an irrigation system
- Changes to connected plumbing equipment
- A notice from your water provider requiring testing or repair
A failed test does not necessarily mean the entire plumbing system needs replacement. In many situations, the assembly may be serviceable or repairable depending on its condition and design.
Modern Backflow Prevention and Plumbing Technology
Today’s plumbing professionals have access to more advanced diagnostic and testing equipment than was commonly discussed in older plumbing articles.
Modern service may involve pressure-testing equipment, specialized gauges, digital documentation, improved testing procedures, and more detailed inspection methods.
However, technology does not replace proper installation and regulatory compliance. Backflow protection still needs to be selected according to the specific plumbing hazard and applicable local requirements.
Backflow Preventer vs. Check Valve: What’s the Difference?
A check valve and a backflow prevention assembly are not necessarily interchangeable.
A check valve generally allows flow in one direction and restricts reverse flow. A backflow prevention assembly may incorporate one or more check valves along with other protective features designed for a particular level of hazard.
The correct device depends on the application, system design, and applicable plumbing requirements.
What Should You Do If You Need a Backflow Preventer?
If your property has an irrigation system, commercial plumbing equipment, pool connection, boiler, or another potential cross-connection, do not choose a backflow prevention device based only on size or price.
A qualified plumbing professional can evaluate the system and determine:
- Where the potential cross-connection exists.
- What type of backflow condition could occur.
- What level of protection is required.
- Which backflow prevention assembly is appropriate.
- Whether testing or certification is required.
- Whether the existing assembly needs repair or replacement.
Proper selection and installation are important because using the wrong type of backflow preventer may not provide adequate protection.
Frequently Asked Questions About Backflow Preventers
What is the purpose of a backflow preventer?
A backflow preventer is designed to help stop contaminated or non-potable water from flowing backward into a potable water supply.
What causes water backflow?
Backflow can occur because of backsiphonage, backpressure, or other changes in plumbing-system pressure that cause water to move opposite its intended direction.
Does every house need a backflow preventer?
Not necessarily. Requirements depend on the property’s plumbing configuration, potential hazards, local regulations, and water-provider requirements.
Does an irrigation system need backflow protection?
Many irrigation systems require backflow protection because irrigation water can come into contact with soil, fertilizers, pesticides, and other contaminants. The required device depends on the system and local requirements.
How often does a backflow preventer need to be tested?
Testing frequency varies according to the device, application, local regulations, and water authority requirements. Some systems require annual testing.
Can a backflow preventer be repaired?
Some backflow assemblies can be repaired when replacement parts are available and the assembly remains suitable for the application. A professional can determine whether repair or replacement makes more sense.
What happens if a backflow preventer fails a test?
A failed test means the assembly may not be operating as required. Depending on the cause, it may need cleaning, repair, adjustment, or replacement, followed by any required retesting.
Protect Your Water Supply With Proper Backflow Prevention
Backflow is more than a simple plumbing inconvenience. It can create a potential pathway for contaminated water to enter a potable water system, which is why proper cross-connection control and backflow prevention are important for many residential, commercial, and irrigation systems.
The right backflow preventer depends on the plumbing application, potential hazard, system design, and local requirements. Professional installation, inspection, and testing can help ensure that the appropriate protection is in place.
If you need help with backflow prevention, testing, installation, repair, or other plumbing services, A to Z Statewide Plumbing can evaluate your system and help determine the appropriate solution.
Call A to Z Statewide Plumbing at 1-800-930-1123 for professional plumbing assistance.
