Toilet Backflow Preventer and Check Valve Guide

A toilet backflow preventer is a device installed to prevent cross-contamination of water. It makes sure that contaminated water does not head back to the main water supply. There are various methods by which you can prevent the backflow of water. Cross connections are rated under three degrees of hazards as follows.

Toilet Backflow Preventer
  • High Hazard: This includes where the water supply system is contaminated and has the potential to cause death.
  • Medium Hazard: This involves causing health issues related to the contamination of water.
  • Low Hazard: If there is no endanger to health or cause injury, but still constitutes a nuisance, then that contamination falls under this section.

Different local codes may require backflow prevention to safeguard the water supply. You can check with your plumber to learn more about the legal requirements. Now let’s find out more about toilet backflow prevention. 

What is Anti-siphon or Backflow Prevention?

Anti-siphon prevention is a regulation code used to keep homes and buildings safe from low water pressure. Usually, the bathroom water system is connected to the community water supply. The system functions properly under the steady pressure of this water supply. But if the water pressure drops due to some reason, it will create a huge impact. This sudden pressure drop can occur in certain situations such as when the local fire department uses water to put down a fire. There is more chance for the water in pipes to flow backward in this case. 

As a result, any debris in the water supply system can flow back into the plumbing system and backflow to your house. If backflow occurs, you will even notice that the tank cleaner used on older toilets will get into the water supply and come out of your sink or bathtub. This shows the importance of backflow prevention in toilets. 

How to Prevent Toilet Backflow?

Modern toilets come with anti-siphon prevention and you should know whether your toilet is protected against backflow. To check this, see the ballcock (the refill valve in the toilet tank) for the terms “anti-siphon” or “code-approved”. If there is no such indication, your fill valve may not be safe against backflow. It is better to call a professional plumber and check the system to determine whether your toilet prevents backflow or not.

Toilet backflow can be prevented easily by installing a one-way backwater valve like a check valve or a backflow preventer. You don’t need to worry about extra protection since the bathroom water line doesn’t contain drinking water. A simple check valve will do the task in most cases. But some areas require a sewer backflow preventer if the toilet is close to the plumbing of the water supply. If the plumber considers that the backflow is too much for the check valve to handle, then you will have to install a double check valve or a backflow preventer. Although these will cost more than a standard check valve, they provide an extra level of protection.

What Are the Different Kinds of Backflow Prevention?

There are several ways in which you can prevent the backflow of water. The main methods are as follows.

  • Air gaps
  • Break tanks
  • Double check valves
  • Reduced pressure zone device
  • Pressure vacuum breaker
  • Single check valve (testable)
  • Double check valve detector assembly
  • Reduced pressure zone detector assembly
  • Single check valve detector assembly

Toilet Backflow Preventer or Check Valve – Which is Better?

Both check valves and backflow preventers are ideal solutions to prevent backflow at home. But a backflow preventer would be more effective with a special design made specifically for the purpose. But it is more expensive than a normal check valve and requires more space for piping. 

A water line check valve will be a suitable option for most houses. If there is a large amount of water coming up the sewer line and reverse water flow, you can install a double-check valve. Then there will be a valve connected to the city sewer and the water system. 

Toilet Backflow Preventer

Frequently Asked Questions

Where Do You Install a Sewer Backflow Preventer?

A sewer backflow preventer valve is installed in the sewer line ahead of any fixtures. In any case, where sewage is being forced back into the home during a flood event, the flapper valve within the valve closes to prevent the sewage from entering the home.

Are Backflow Preventers Worth It?

It is always recommended to install a backflow preventer to keep your water system safe. The water can be contaminated with debris and harmful particles once the lines cross-connect. So it is worth investing in the installation of backflow preventers to keep your family safe. It will keep your drinking, bathing, and cleaning water safe.

How Do I Know if I Have a Sewer Backflow Preventer?

If you are not sure, whether you have a sewer backflow preventer, you can take a look around your basement. Backwater valves are usually located on the floor under a cover that can easily be removed for maintenance. The cover will mostly be round, and may also have a rectangular panel on top. If you have a sump pump in your basement, the backwater valve will most likely be close by.


How Much Does It Cost to Put in a Backflow Valve?

The average cost of installing or replacing a backflow preventer is around $300. But the actual costs for the project will be between $135 and $1,000 based on the size of the system and the requirement. The type of valve, other materials, and labor will determine the total cost.

How Much Does It Cost to Have a Check Valve Installed?

The average cost of installation for a check valve will be between $135 and $1,000 depending on the system. The components costs between $35 and $600 and the labor costs are between $100 and $400. You can expect to pay something between $70 and $250 for a check valve.

Is a Backwater Valve the Same as a Backflow Preventer?

Backwater valves and backflow prevention devices have different designs. Backwater valves protect you from the public water system. They are often used to prevent sewage from flowing back to the house. The backflow preventers are designed to protect the public water system from the residents. 

How Long Do Backflow Valves Last?

The backflow devices are considered “non-testable” since their performance cannot be tested. They can only be maintained by rebuilding or replacing the device once every five years.


Backflow prevention devices are installed in toilets to prevent contamination of water in your home. It protects you from sewage gases, muddy water, and other contaminants that may flow back into the water supply during low-pressure situations. So, check your toilet water filling system to make sure that it is safe from possible backflow. If not, you install a toilet backflow preventer or a check valve. Despite the cost, it will save you from potential health risks and prevent any damage to your toilet.