Upcoming Building Code Changes

On May 1, 2024, the National Building Code - 2023 Alberta Edition will take effect. Please follow the link for more information if you are planning to build this Spring.

Backwater Valve

Sample of backwater valve

What is a backwater valve?

The drainage system inside your house channels wastewater from your sinks, laundry, shower, and toilet through pipes that connect to a main sanitary sewer pipe under your house.  This pipe leads to the property line where it connects with the Town's main sewer line.

A mainline backwater valve can help prevent sewage in an overloaded main sewer line from backing up into your basement. Placed directly into the sewer lateral in your basement , the valve automatically closes if sewage backs up from the main sewer.

How do I maintain my backwater valve?

Check out this video on how to maintain your backwater valve.  You may skip the ads at the beginning of the video.

Directions on how to clean your backwater valve:

  • Locate your backwater valve and remove the plug or panel.
  • Shine the flashlight around the area and look for debris. Debris stuck in the gate can cause the sewer backwater valve to stop working. Clear the area.  
  • Flush the valve with a bucket of water to clear debris from the gate area. If deposits or grease or other debris remain, scrubbing may be required.
  • Once clean, move the gate back and forth to make sure it moves without any problems. If it's stiff or you see rust, oil it a little bit with food grade oil.
  • Check the O-ring on the backwater valve. If it's cracked or damaged, replace it.  Some of the newer backwater valves may not have an O-ring.
  • Properly reinstall cleanout plug or panel when maintenance & inspection are completed.

Is there a way to install an alarm on my backwater valve?

Yes, it is recommended that an alarm be installed that will go off if your backwater valve has a high level of water in it.  By installing an alarm you would receive a notification that something is wrong and that you should stop creating sewage in your home (flushing toilets, running dishwasher, & using sinks and showers etc.).  The above video link explains how the alarm system would work.

How do I know if I have a backwater valve?

If you aren't sure, take a look around your basement — backwater valves are usually located in the floor and have a cover that can easily be removed for maintenance. The cover itself is likely round, but there may also be a rectangular panel on top. If you have a sump pump, the backwater valve is likely close by.  Backwater valves became a requirement in approximately 1989.

Is a backwater valve and backflow preventer the same?

These are different devices.  They sound similar enough that the confusion is not unfounded.

A backwater valve is a device that’s installed on your sewer drain so as to prevent the backup of sewage water back into the drain pipe, which would otherwise flood your basement or wherever the drain pipe connects. 

A backflow preventer on the other hand is to prevent the backflow of clean water back into a water source. Typically a water supply line is under heavy pressure and there is little chance of the water backing up, but under high-demand or problems such as a burst main this pressure will drop allowing for the potential backflow of contaminants into the water supply. To stop this backflow preventer devices are installed in high risk areas to keep the water supply fresh and clean.

To recap; backwater valves prevent the backflow of sewer water into your drains, and backflow preventers prevent the backflow of potentially contaminated water into the water supply lines.

How can I protect my home from flooding?

Intact Centre created an infographic on how to best protect your home from flooding. The link is available here.

Not all actions will be applicable to each home.  Completing the steps shown in the pamphlet does not guarantee the prevention of flooding.  These steps could reduce the risk of flooding.

How do I protect my backwater valve?

Beware that if a plumbing snake is used, a backwater valve could be damage if the flap is not first removed. A homeowner must inform a hired contractor if they think that have a backwater valve installed to prevent damages.


Residents are encouraged to contact your local plumber if you need assistance locating or maintaining your backwater valve. They will be able to help guide you in the right direction of the code and permit requirements and what's best for your home. As well, they will have field experience with these devices and will be able to give you some more practical tips.

As well, you may contact:

Josh Solowan, Plumbing & Gas Safety Codes Officer
The Inspections Group Inc.
Ph. 780-220-2182