Anti-Siphon Valve vs Backflow Preventer: Which One Do You Need?

When you get into plumbing, you learn a whole new vocabulary. You may also become confused by terms like anti-siphon valve vs backflow preventer, which are often used interchangeably. What do these terms mean, and what kind of valve do you need for your project? 

A backflow preventer is an umbrella term that describes any system that prevents water from returning to the public water supply after being used through an irrigation system. An anti-siphon valve is a specific type of backflow preventer. Unless you have experience with irrigation systems, these terms are likely confusing. 

This article will help you distinguish between an anti-siphon valve vs backflow preventer.

What Is A Backflow Preventer?

Before comparing an anti-siphon valve vs backflow preventer, it’s essential to learn what a backflow preventer is.


Keeping landscape plants healthy is critical, but so is maintaining the quality of potable water that humans consume. An irrigation system that separates the water from drinking water prevents contamination that may cause illness. That is why a backflow preventer is a must on every irrigation job.

When you don’t install backflow preventers on irrigation systems, soil and other impurities may contaminate the public water. These devices help to prevent the contamination of public water supplies and provide clean water. 

The presence of a backflow preventer ensures that irrigation water is free of impurities and pesticides. If a backflow preventer is not installed, the negative pressure in the water supply system may cause contaminants to enter the water. 

Now that we know what a backflow preventer is, let’s learn more about anti-siphon valve vs backflow preventer.


Do You Need A Backflow Preventer On Everything?

Specific applications don’t require a backflow preventer. It will help if you use them with any hose connection point, such as your tap. The water that comes through an irrigation system, for instance, has to be kept away from soil and other contaminants that can be present. 

Every state has its laws regarding backflow prevention, so it’s always wise to know yours. Municipal ordinances might be challenging to read, but you should be okay if you understand what to look for. 

Whenever you hear the phrase ‘cross-connection control,‘ they refer to backflow prevention. 

Now that we’ve gotten a reasonable idea of what backflow prevention is, let’s learn further about anti-siphon valve vs backflow preventer.


What Is An Anti-Siphon Valve?

Before comparing anti-siphon valve vs backflow preventer, it’s essential to learn what an Anti-Siphon valve is.


Residential water supply systems typically employ one of the most popular backflow preventers: the anti-siphon valve. It is simple to install and economical. 

An anti-siphon valve uses an atmospheric vacuum breaker to create an anti-siphon effect. These valves prevent the re-entry of water from the outside into a system. An atmospheric vacuum breaker in anti-siphon valves prevents suction that leads to contaminated water infiltrating residential water systems.

They are also known as AVBs (Atmospheric Vacuum Breakers) in some areas due to their suction-breaking ability, but they are not AVBs

Hopefully, after learning about anti-siphon valves, you can compare anti-siphon valve vs backflow preventers easily.

Is An Anti-Siphon Valve Right For You?

When it comes to anti-siphon valves, there are many to select from, but they’re not guaranteed to be the best option for everybody. These devices are widely used, but they have several limitations. Knowing what to look out for can assist you in determining whether or not this is the right choice for you. 

Some of the most significant limitations include the following:

  • You must install anti-siphon valves about six inches above the ground, which means they can’t work for underground irrigation systems. If you like to hide the valve, we recommend planting a shrub or something close to it to obscure it from sight.
  • You have to link these valves to the water source. The ASV will be where your irrigation system connects to the hose. Consider it as a “hub” for water.
  • You cannot install them upstream of other backflow preventers. This will force them not to work.
  • Under no case should you ever attempt to install an anti-siphon valve in an area where it could be submerged underwater. This type of backflow prevention is a terrible choice in areas where floodplains exist.
  • Some cities and countries have building codes that dictate the backflow prevention required to stay up to code. If your building codes inform you that you cannot use an ASV, hear them.

It will help if you go through all these limitations before deciding between an anti-siphon valve vs backflow preventer.


How To Choose The Best Type Of Backflow Preventer?

Now we will learn how to decide which is better: anti-siphon valve vs backflow preventer. 

Irrigation specialists can help you determine the type of backflow prevention device you need for your home’s water supply system. You may need to consult with a local expert to decide which backflow prevention devices are allowed in your area if your irrigation system connects to the potable water supply. 

You may also learn about the different types of backflow prevention devices to find out what each does. Once you’ve selected what device you want to use: anti-siphon valve vs backflow preventer, you should check the local regulations to see if it’s permitted.

What Are The Most Common Types Of Backflow Preventer?

Now that we’ve gotten a reasonable idea of what backflow prevention is, it’s good to understand some of the different kinds of backflow prevention that do not include anti-siphon valves.

  • Pressure Vacuum Breaker. This is almost similar to anti-siphon valves, except you only need to utilize one. If you have anti-siphon valves, you may need as many as six to shield your irrigation system.
  • Double Check Valve Assemblies. These are dual-mechanism backflow prevention instruments that have the bonus of being able to be installed underground. They’re incredibly efficient at what they do.
  • Atmospheric Vacuum Breakers. AVBs, as they’re known, are best compared to stripped-down anti-siphon valves. Here, you require one AVB for every control point in your irrigation system. They’re very affordable, but that doesn’t make them economically feasible all the time. It can be downright pricey after a specific point and may even donate to over-irrigation.
  • Reduced Pressure Assembly. Do you have an area that is highly hazardous in terms of contaminants? Then you need a reduced pressure assembly. These models are specifically made to handle high-hazard, high-waste situations like commercial farms.

Besides the anti-siphon valve vs backflow preventer, you can use the backflow preventers mentioned above to help prevent pollution or contamination of water.

How Much Does A Backflow Preventer Cost?

When learning the differences between an anti-siphon valve vs backflow preventer, it’s crucial to know how much a backflow preventer costs. 


The price of a backflow preventer can vary greatly regardless of what kind of system you want to use it in. A backflow preventer can range from $35 to over $900 for the part alone, with Reduced Pressure Assemblies being the most expensive option. 

The installation cost for the backflow preventer may also vary. If you install it yourself, you won’t have to worry about it. On the other hand, if a professional installation is required, you’ll have to pay between $30 and $250. 

Since installing backflow prevention in your garden is one of the most costly aspects of your irrigation system, it will cost between $75 and $1150.


Some municipalities are so serious about keeping their water supplies clean that they take harsh measures against contamination. You can safeguard residential water supplies from contamination by employing anti-siphon valves. Public water systems, on the other hand, benefit from backflow preventers. 

Both the devices (anti-siphon valve vs backflow preventer) are necessary if you want to safeguard every household or irrigation system. Hopefully, this guide assists you in understanding the difference between anti-siphon valve vs backflow preventer.

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Michael Bowen

Michael Bowen

Michael Bowen is an ambitious entrepreneur who has been in the business of building homes since he was 19. Michael's commitment to honesty, integrity, and high-quality workmanship has earned him a reputation as one of the best in the business.

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