Backflow Prevention 101: Protecting Your Water Supply

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Backflow prevention is crucial for protecting the purity of your drinking water and the public water supply. Backflow prevention devices and methods can be installed in any plumbing system, even on garden hose connections, to prevent contamination of potable water.

Without these devices, sewage and other contaminants can flow into your drinking water or back up into your home or business, causing extensive property damage. Backflow can even expose you to legal liability for contaminating potable water supplies.

What is Plumbing Backflow?

Backflow occurs when water in your plumbing system reverses direction, allowing contaminated water to flow back into your clean water supply. While plumbing systems are designed for water to flow in one direction only, certain conditions can cause this dangerous reversal whenever there is a significant change in pressure, either positive or negative, within the system.

Types of Backflow

The two primary kinds of backflow are backpressure backflow and backsiphonage backflow.

Backpressure Backflow

Backpressure backflow is caused by positive pressure downstream of the clean water supply in a plumbing or other pressurized system. This pressure pushes sewer or other contaminated water to reverse flow into the clean water upstream.

One example of backpressure backflow is when a boiler’s temperature increases, creating excessive pressure on the water supply and pushing contaminated water upstream.

Backsiphonage

Backsiphonage occurs in two main situations: when water main pressure drops due to breaks or repairs, or when high water usage (like firefighting) creates excessive system demand.

The pull on a fire hydrant during firefighting creates a vacuum that sucks the system’s water in the reverse direction, contaminating the potable water. Marine fire suppression, where overhead sprinklers put extreme demand on the water supply, is another example of backsiphonage. 

A garden hose submerged in non-potable water, such as a pool, can also be subject to backsiphonage. A loss of main pressure can cause the pool water to be siphoned into your drinking water.

Backsiphonage can also occur at cross-connections between clean and dirty water, like when a dishwasher’s contaminated water is siphoned into clean water lines by negative supply-side pressure.

What Causes Backflow?

Backflow is caused by pressure changes within the plumbing system, which can occur at cross-connections, or due to various types of system failures.

Changes in Water Pressure

Positive downstream pressure in a plumbing or piping system can lead to backpressure backflow by pushing contaminated water backward into clean water lines.

Negative supply-side pressure can result in backsiphonage backflow by sucking contaminated water into clean lines.

Cross-Connections

Cross-connections allow clean water lines to be connected to contamination sources. The most common example is a garden hose connected to your water supply that is then submerged in non-potable water.

If a hose immersed in a bucket of detergent experiences a negative change in pressure (backsiphonage), it could suck the detergent water into your drinking water supply.

Another example is when clean water piped to a chemical rinse tank experiences greater pressure from the tank. This positive pressure (backpressure) will push the chemical-laden tank water into the clean water line.

System Failures

Backflow can occur from failures including broken water mains, power outages, and pressure differences within the system.

Power outages can cause bacteria to grow in water tanks when water is left stagnant. Once power is restored, this contaminated water is pushed through the system, creating backpressure backflow. Power outages can also cause water pumps to stop working, resulting in water flowing backward. 

Pressure differences in your home’s plumbing can also lead to backflow. Many appliances depend on water pressure to operate, but if that pressure is higher than your water supply, it can overburden the lines and cause backpressure backflow.

Effects of Backflow

Backflow is a serious issue that can contaminate fresh water supplies for entire cities, cause property damage to homes and businesses, and create legal liability for those who allow it.

Contamination of Water Supply

Since plumbing systems are designed for one-way water flow, a reversal can allow contaminated water to enter the clean water used for drinking and bathing. This can have serious health consequences.

Under the right conditions, a homeowner’s backflow can also contaminate the public water supply, threatening the health and safety of entire communities.

Property Damage

Backflow can damage plumbing, appliances, fixtures, heating, and cooling systems, requiring expensive repair, remediation, or replacement.

It can also cause extensive water damage to homes and possessions. Because this water is contaminated, professional intervention is required for safe clean-up. Ongoing backflow can even damage yards and foundations.

Legal and Regulatory Consequences

The Uniform Plumbing Code (UPC), a model code designed by the International Association of Plumbing and Mechanical Officials (IAMPO), governs the installation and inspection of plumbing systems. It is the only plumbing code designated as an American National Standard and is enforceable.

Chapter 6 of the UPC addresses backflow prevention directly. Penalties for violating the UPC can include fines, permit revocation, plumbing license revocation, denial of insurance claims, and even legal costs.

The UPC provides general guidelines, but specific backflow prevention requirements vary by location. One great resource is buildingsguide.com/build/building-codes-by-state. You can also search your municipality’s website for plumbing codes.

Not all homes require backflow preventers. However, sprinkler systems connected to your well, supply line, or the public water system create cross-connections with your potable water. Whether you have sprinklers or not, it’s wise to have your system inspected for cross-connections and potential backflow.

The same principle applies to fire sprinkler installation. Take appropriate measures to avoid creating cross-connections or potential backflow situations. For existing systems, a fire sprinkler inspection should determine the best means of regulatory compliance and backflow prevention.

Non-compliance consequences vary by state and locality but can include fines and attorneys’ fees. According to the American Water Works Association, damages from breaching your duty to prevent backflow can include medical expenses, loss of income, property damage, loss of market value, repair costs, court costs, etc.

In an example listed by the EPA, a public water system (PWS) experienced a large-scale cross-connection and backflow problem during a fire protection event. Aqueous firefighting foam was pushed into approximately 40,000 homes because the PWS lacked a backflow prevention assembly, exposing it to liability. 

In another example, two companies violated the Texas Health and Safety Code by allowing contaminated water backflow into the City of Corpus Christi’s water supply. Their violations cost them $2.6 million.

How to Fix Backflow Issues

The first step in fixing a backflow issue is identification. Then seek immediate professional help.

Identifying Backflow Problems

Signs of backflow in your plumbing system include:

  • Discolored water containing foreign particles like dirt or rust
  • Visible debris floating in your water supply 
  • Bad odors such as sewage or sulfur smells
  • Low water pressure
  • Gurgling noises caused by trapped air trying to escape a negative pressure zone in the plumbing
  • Slow drains, including in the kitchen, shower, and dishwasher
  • Bad taste (Never drink water with an odd or foul taste, as it could have serious health consequences)
  • Repeated leaks

Immediate Solutions

Once you’ve detected backflow, immediately call a licensed, professional plumber or backflow specialist. This is not a DIY fix.

Know the location of your main water supply shut-off in case of a backflow accident. Shutting off the water immediately can protect you from property damage and liability.

Professional Intervention

Hire a professional to handle backflow issues. Licensed plumbers and backflow specialists have the knowledge and experience to diagnose and treat backflow problems, accidents, and emergencies. They can repair plumbing systems and install necessary backflow prevention devices and solutions.

Preventing Backflow

There are a number of backflow prevention techniques and devices that can maintain proper directional water flow, including air gaps, check valves, reduced pressure zone assemblies, double check valve assemblies, pressure vacuum breaker assemblies, and hose bibb vacuum breakers.

Installing Backflow Prevention Devices

An air gap is a physical separation between the incoming water supply and your plumbing system. This gap helps maintain the proper pressure to prevent backpressure or backsiphonage backflow. For example, an air gap in a sink can prevent dirty water from entering your dishwasher.

However, air gaps may not be practical in every situation and can be easily bypassed.

Check valves are one-way valves that prevent water from reversing course and causing backflow.

Reduced pressure zone assemblies, also called reduced pressure principle assemblies, are backflow preventers consisting of two independently operating check valves with a pressure differential relief valve between them. If either check valve fails, the relief valve diverts contaminated water from the clean water supply. These assemblies work against both backpressure and backsiphonage backflow.

Pressure vacuum breaker assemblies are backflow prevention devices that utilize a check valve and air inlet valve to prevent backsiphonage. The air inlet valve allows air in to break the vacuum causing backsiphonage. However, this assembly does not prevent backpressure backflow.

Double check valve assemblies consist of two independent check valves ensuring water flows in only one direction. They prevent both backsiphonage and backpressure backflow but should only be used to isolate non-health hazards.

Hose bibb vacuum breakers are pressure vacuum breakers made specifically for garden hose connections. They screw directly onto the threads for easy installation. When there’s water pressure in the hose, the air inlet valve remains closed. But if supply pressure abruptly cuts off, the air inlet valve opens, releasing hose pressure to prevent backsiphonage into your home’s clean water.

Regular Maintenance and Inspections

The Uniform Plumbing Code (§603.4.2) requires testing of backflow preventers by a certified backflow assembly tester upon installation, repair, or relocation, and at least annually thereafter. More frequent testing may be required if mandated by the Authority Having Jurisdiction (AHJ), i.e., your local, state, or municipal government.

Most professional plumbers recommend having your entire plumbing system inspected at least every two years.