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What is a Backflow Preventer? (And Do I Need One?)

The backflow preventer is an unsung hero of plumbing that helps keep contamination out of your water supply. Many people don’t know how they work or even that they exist — but they’re critically important for your property and your community, all the same! Let’s get the knowledge flowing and dive into what you need to know about backflow preventers.

What Does a Backflow Preventer Do?

Backflow refers to water in a plumbing system flowing in the wrong direction. More specifically, it means dirty water (such as water from your lawn or bathroom) flowing back into a clean water supply line.

Backflow happens when pressure changes in your water line, causing water to flow the wrong way. The cause can be either pressure that’s too high on your property (called backpressure) or too low on the supply side (called back-siphonage). Either way, it can draw contaminated water into your public water supply, which threatens everyone’s health and safety. That’s why backflow prevention is so important.

How Does a Backflow Preventer Work?

We’ll spare you the nitty-gritty details — but it’s useful to know the basics of how backflow preventers work. Here’s a quick summary: 

  1. The backflow preventer is installed on your main water line and uses a series of valves that flow in only one direction.
  2. The check valves allow clean water to flow into your home or business when system pressure is normal.
  3. If the system experiences back pressure or back-siphonage, the check valves prevent it from flowing back into the water supply. Instead, the dirty water is discharged through the relief valve onto the ground or into a drain. (Some types of backflow preventers, known as double check-valve systems, don’t have a relief valve.)
  4. A test valve allows the backflow preventer to be periodically tested. (Most local governments require annual backflow testing and monitoring on all backflow preventers.)

If you really want the specifics, check out the American Water Works Association’s backflow preventer standards. Otherwise, let’s get down to a more practical question: Does your property need a backflow preventer?

Do I Need a Backflow Preventer?

Whether you need a backflow preventer depends on what type of property you have. Rules can vary according to where you live, so be sure to check your local backflow prevention laws. 

Commercial Properties: Yes

  • Nearly all US commercial and institutional properties, large and small, are required by state and/or local laws to have backflow preventers and to have them inspected annually.

Single-Family Homes: Sometimes

  • Single-family homes usually aren’t required to have a main water supply line backflow preventer. The exception: If your home has an irrigation system, swimming pool, well, or another outdoor device that’s connected to a main water line, you’ll often need a backflow preventer. Local municipalities require an annual backflow inspection by a certified backflow expert.

Multi-Family Homes: Yes

  • Most multi-unit housing structures are required to have backflow preventers. 

Choosing a Backflow Preventer

Several different types of backflow prevention devices are available, depending on the type of backflow control your property needs: 

  • Main Backflow Preventer: The standard type of backflow preventer that sits on your main water line.
  • Hose Bib Backflow Preventer: This smaller device, also called a vacuum breaker, attaches directly to your outdoor hose spigots to prevent dirty water from flowing back into your home’s clean water supply. For instance, if you are adding water to a pop-up above-ground swimming pool and you place the flowing garden hose into the pool, if backflow-siphonage were to occur, that dirty pool water could be siphoned back into the municipal water supply pipeline. Unlike other types of backflow preventers, a vacuum breaker is easy to install yourself.
  • Sewer Backflow Preventer: Also called a backwater valve, this device is installed on your property’s sewer line and designed to prevent combination sewage backups during heavy rainfall or sewer system overflows.

Backflow Preventer Installation

Unfortunately, installing a backflow preventer is not a job for a weekend DIY project. First, in most places, local laws will actually require that you use a licensed plumber with a backflow certification to install your backflow preventer. In addition, it’s a more complicated task than it looks like, and installing one the wrong way could contaminate your clean water supply. And if your backflow preventer is leaking or otherwise experiencing problems, a plumber needs to be your first call, without a doubt. 

That’s OK — Roto-Rooter is your ace in the hole for every plumbing job, including backflow preventer installation, inspection, and repair. We’re a licensed and insured team of professionals with decades of experience in backflow prevention. Call our service team now at 800-768-6911 or schedule your appointment with our pros online.



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