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Backwater Valves – How They Work, Costs and Repairs


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Eugene Kushmarak

Please meet Eugene, one of our basement flood experts. He started his career from the bottom, digging trenches, working his way up to contractor, supervisor. Learn More About Eugene Kushmarak

Ever worried about your basement flooding during a sudden downpour in Toronto? Given the city’s unpredictable weather, this concern is all too common. Fortunately, you can protect your home from unwanted water damage by installing a backwater valve. This simple device is designed to keep floodwaters at bay, offering a crucial line of defense for your home. Let’s dive into how a backwater valve can safeguard your property from unexpected flooding!

What is a Backwater Valve?

A backwater valve, sometimes known as a backflow valve or sewer backup valve, is an essential device installed on the main wastewater line from your house to the public sewer system. It ensures that water and sewage flow only one way — away from your home. This is crucial in areas like Toronto, where heavy rainfall can overwhelm sewer lines, causing potential backflows into homes.

Backwater Valve Installation

Municipalities often require or recommend the installation of backwater valves, and some provide subsidies for them, especially in homes with basements or where the ground level is near street level. According to the National Plumbing Code, homes with any fixtures below street level must have a backwater valve to prevent backups.

It’s important to note that backwater valves differ from backflow preventers, which are installed on potable water lines to prevent contaminated water from reversing into the clean supply. Both devices are critical in preventing water-related damages but are used in different contexts.

How Does a Backwater Valve Work?

A backwater valve works using a simple but effective mechanism. It has a flap inside it, which is part of the drain pipe that carries wastewater from your home to the sewer. Normally, this flap stays open, letting wastewater flow out smoothly.

However, if sewer water starts to back up towards your home because of heavy rain, this pushes the flap to close automatically. This stops the sewer water from entering and flooding your home.

Once the sewer water stops backing up, the flap opens again on its own, allowing wastewater to flow out as usual. This automatic function keeps your home safe without needing you to do anything.

When Do I Need a Backwater Valve?

A backwater valve is essential for protecting below-grade areas like basements from sewage backups, especially when connected to sanitary drains. Here’s when to consider installing one in your Toronto home:

  • Home Age: If your home is over 30 years old, it might not have a backwater valve.
  • High-Risk Area: Homes in flood-prone zones or with high water tables should have a valve.
  • Local Sewer Backups: If there have been sewer backups in your neighborhood, it’s a wise precaution.
  • Previous Backups: If your home has had a sewer backup before, installing a valve can prevent future issues.
  • Recent Renovations: If you’ve recently renovated or finished your basement, installing a valve can protect your new investment from water damage.
  • Insurance Recommendations: Some insurance companies recommend or require the installation of backwater valves to qualify for or improve coverage terms related to water damage.


Considering these factors can help you decide whether to consult with a professional like Aquatech Waterproofing for an assessment and potential installation.


How Much Does It Cost To Install A Backwater Valve in Toronto

Installing a backwater valve in Toronto typically ranges between $2,000 and $5,000 if retrofitting into an existing home. This process involves significant labor, including breaking into the foundation to access the sewer line. However, installing one during new home construction is more cost-effective, generally around $500, as it can be integrated directly into the building plans with less labor required.

What Should You Know About Backwater Valves?

  • Permits and Equipment: Before installing a backwater valve, consult with your local municipality to understand the necessary permits and recommended equipment.
  • Proper Connections: Ensure that your home’s drains and downspouts are not connected to the weeping tiles or sanitary sewer. Disconnecting may require installing a sump pump.
  • Professional Installation: Use a licensed plumber for the installation to ensure compliance with local codes and to handle any permits.
  • Accessibility: Keep access to the backwater valve clear for maintenance and inspection. Avoid covering the valve with flooring or other permanent fixtures.
  • Routine Checks: Know the location and function of your backwater valve. Regular maintenance is vital to prevent blockages and ensure smooth operation.

How to Repair a Backwater Valve

Repairing a backwater valve is crucial for ensuring it continues to protect your home effectively from sewage backups. Here are general steps to guide you through the process:


  1. Identify the Issue: Before any repair, determine what problem the valve is facing. Common issues include stuck flaps, debris blocking the valve, or damaged seals.
  2. Shut Off the Water: To safely conduct repairs, always shut off the main water supply to prevent any accidental water flow or backup during the process.
  3. Access the Valve: Remove the cover of the backwater valve. This might involve clearing any ground covering or debris around the access point.
  1. Clean the Valve: Often, simply cleaning the valve can resolve issues. Remove any dirt, debris, or objects that might be obstructing the flap or the flow of water.
  2. Inspect Components: Check the flap, seals, and floaters. Replace any components that are worn out or damaged. Ensure the flap moves freely and seals correctly when closed.
  3. Test the Valve: Once cleaning and any replacements are made, reassemble the valve and turn the water back on. Monitor the valve during usage to ensure it operates correctly and no longer allows backflow.
  4. Seek Professional Help: If the problem persists or the repair is beyond your comfort zone, it’s advisable to call a professional plumber. They can provide a more thorough inspection and perform complex repairs if needed.

Regular maintenance and timely repairs of your backwater valve are key to preventing costly damage from sewer backups. Always consult with a professional if you’re unsure about the process to ensure the job is done safely and effectively.

How to Maintain a Backwater Valve

Maintaining a backwater valve is essential to ensure it functions properly and protects your home from sewage backups. Here are some simple steps to keep your backwater valve in good condition:

  • Inspect Regularly: Check the valve at least annually for any signs of wear, damage, or obstruction. This is especially important before the rainy season.
  • Clean Thoroughly: Remove the cover of the valve and clear out any debris, dirt, or foreign objects that could prevent the valve from closing properly.
  • Check the Flap and Seals: Ensure the flap moves freely and the seals are intact. Replace any parts that appear worn or damaged to maintain a good seal.
  • Test Operation: After cleaning and inspection, test the valve by running water through it to make sure it opens and closes correctly.
  • Avoid Chemicals: Steer clear of using harsh chemicals for cleaning that could corrode or damage the valve components.
  • Document Maintenance: Keep a record of all inspections, cleanings, and repairs. This documentation can be valuable for warranty purposes and can help troubleshoot future issues.


Regular maintenance ensures your backwater valve will work effectively when needed, reducing the risk of costly water damage to your home.

Contact Aquatech Waterproofing for Your Backwater Valve Installation Today!

Protect your home from unexpected flooding with Aquatech Waterproofing. Our experienced team ensures a seamless and reliable backwater valve installation, tailored to meet the specific needs of your Toronto home. Opt for Aquatech’s expert service to keep your basement dry and secure. Reach out today and secure your home against the elements!

FAQs About Backwater Valves

While it’s technically possible for a handy homeowner to install a backwater valve, it typically requires professional skills and knowledge of local building codes. It involves significant work, including cutting into the main sewer line. Most homeowners opt for a licensed plumber to ensure the job is done correctly and up to code.

Yes, installing a backwater valve can potentially lower your home insurance premiums since it reduces the risk of water damage from sewer backups, which are costly to clean up and repair. Some insurance providers may offer discounts or incentives for homes equipped with flood prevention devices like backwater valves. It’s best to contact your insurance provider to discuss how installation could impact your rates.

Some municipalities have specific regulations requiring backwater valves in certain areas, particularly those prone to heavy rainfall or flooding. These regulations vary by location, so it’s important to check with your local building department or municipal office to determine if there are legal requirements or building codes that apply to your property.

Yes, backwater valves can be installed in nearly any home, although the complexity and cost of installation may vary based on the home’s existing plumbing layout and local building codes.