The backflow preventer you need depends on your system’s use and the level of risk involved. For a typical residential lawn or garden irrigation system, a Pressure Vacuum Breaker (PVB) is often sufficient. For commercial plumbing or fire sprinkler setups, a Double Check Valve Assembly (DCVA) is more common. If your system poses a higher contamination risk—such as involving chemicals or industrial runoff—a Reduced Pressure Zone (RPZ) device is usually required. The safest option is always determined by a certified plumber who understands your setup and local regulations.
Backflow prevention is one of those things you don’t notice—until something goes wrong. If you’re a homeowner, property manager, or business owner, having the right backflow preventer in place can protect your water supply, keep you compliant with code, and prevent serious health hazards.
Let’s break down everything you need to know, step by step.
What Is a Backflow Preventer?
A backflow preventer is installed on your plumbing system that stops water from flowing in the wrong direction. It protects your clean water supply from contamination in case of pressure changes.
When there’s a sudden drop in water pressure, such as from a broken main or heavy water usage elsewhere—dirty water can be pulled back into your drinking water system. That’s known as backflow, and without a preventer, contaminants like fertilizers, chemicals, or even sewage could make their way into your home’s tap water.
How Do I Know What Size Backflow Preventer I Need?
To determine the correct size of a backflow preventer, match it to the diameter of your pipe and the flow rate of your system. Most homes use ¾” to 1″ devices, while larger commercial systems may require 1.5″, 2″, or more.
You should not estimate sizing. Undersized devices can restrict water flow, and oversized ones may not function correctly. A professional can evaluate your water usage and ensure the device matches your plumbing and local building codes.
What Is the Most Common Backflow Preventer?
The most common backflow preventer for residential use is the Pressure Vacuum Breaker(PVB), especially for sprinkler or irrigation systems. For commercial or light industrial buildings, the Double Check Valve Assembly (DCVA) is widely used.
When contamination risks are higher, like with labs, factories, or properties handling chemicals—the Reduced Pressure Zone (RPZ) device is considered the standard due to its advanced protection.
What Are the Different Types of Backflow Preventers?
There are several types of backflow preventers, each designed for specific levels of risk and system requirements.
1. Air Gap
An air gap isn’t a mechanical device. It’s simply a physical separation between the water outlet and the flood level of a fixture. Think of it as the space between your faucet and a sink basin. It’s the safest form of backflow prevention, but it isn’t always practical.
2. Atmospheric Vacuum Breaker (AVB)
This is a simple, low-cost device used in non-pressurized systems like garden hoses. It works well, but it can’t be used under continuous water pressure.
3. Pressure Vacuum Breaker (PVB)
A PVB prevents back-siphonage in pressurized systems, making it ideal for home irrigation. It must be installed above the highest outlet in the system and requires periodic testing.
4. Double Check Valve Assembly (DCVA)
A DCVA has two check valves that offer moderate protection against both backpressure and back-siphonage. It’s used in systems that pose a potential—but not serious—risk of contamination, like fire sprinklers or commercial boilers.
5. Reduced Pressure Zone (RPZ) Assembly
The RPZ offers the highest level of protection. It includes two check valves and a relief valve that opens to discharge water if either check valve fails. RPZs are used where the risk of backflow contamination is significant.
What’s the Difference Between a PVB and an RPZ?
The main difference between a PVB and an RPZ is the level of protection and the type of backflow they prevent.
- PVB devices protect against back-siphonage only and are suitable for moderate-risk uses like lawn irrigation.
- RPZ devices protect against both back-siphonage and backpressure, and they’re required for high-risk applications like chemical systems or health care facilities.
RPZs are also equipped with a relief valve that discharges water when pressure imbalances are detected, making them more reliable for dangerous scenarios.
What Happens If You Don’t Have a Backflow Preventer?
If your plumbing system doesn’t have a backflow preventer, contaminated water can enter your clean supply, putting your household—or even the entire neighborhood—at risk.
Possible consequences include:
- Health risks from exposure to bacteria, chemicals, or waste.
- Fines and legal issues if your system doesn’t comply with local plumbing codes.
- System damage and costly repairs if contamination spreads through appliances or pipes.
In many areas, backflow preventers aren’t optional—they’re a requirement. Annual testing may also be necessary, especially for commercial or high-risk systems.
Do You Need a Professional to Install One?
Yes. Backflow preventers must be installed and tested by licensed professionals in most jurisdictions. Improper installation can result in failure, code violations, and water contamination.
A certified technician can:
- Inspect your system
- Identify the right device
- Handle installation
- Conduct required annual testing
This ensures your system works correctly and meets all local requirements.
Final Thoughts
Choosing the right backflow preventer isn’t about overcomplicating things—it’s about protecting your water and staying compliant. Whether you need a basic PVB for a home sprinkler system or an RPZ for a high-risk commercial setup, getting it right matters.
If you’re ever unsure, reach out to a licensed plumber who knows the local code. They’ll help you avoid the guesswork and install the right solution from day one.
