A backwater valve: A small device that can save you from a major disaster

It only takes a few minutes for a flooded basement to turn into a nightmare. But there’s one small piece of equipment that can make all the difference: the backwater valve. It’s not well known, but it’s one of your best lines of defence against water damage.

A backwater valve lets wastewater flow in one direction only: from your home to the city sewer system. If the system backs up, the valve slams shut, blocking contaminated water from coming into your basement and helping to keep your home dry and safe.

There are several types of backwater valves, but all serve the same critical purpose: preventing claims and costly damage. On August 9, 2024, after the remnants of Tropical Storm Debby hit Quebec, many homeowners learned this the hard way. Montreal’s downtown was hit with over 154 mm of rain, triggering widespread sewer backups across multiple neighbourhoods.

Is a backwater valve easy to install?

Installing one isn’t a DIY job. As the Régie du bâtiment du Québec (RBQ) explains (French only), proper installation (French only) requires expertise and compliance with local regulations. That’s why you’ll need a certified plumbing contractor, recognized by the Corporation of Master Pipe Mechanics of Quebec (CMMTQ), to do the work. This ensures your valve is installed to code and accepted by your municipality.

Also important: the valve must always remain accessible. If it’s hidden behind a wall or under a raised floor, you’ll need to create an access panel or removable door. And once it’s in place, don’t forget about it! Annual inspection and maintenance are strongly recommended to keep it functioning when you need it most.

Sewer backup: Are you covered?

Here’s the catch. Standard home insurance policies usually don’t cover sewer backups. You’ll need to purchase optional coverage, such as an endorsement for water damage caused by sewer or groundwater, for an extra premium.

Some types of backups may be covered by basic insurance, like an “internal” backup caused by blockages in your home’s plumbing system. But if the issue stems from an overloaded municipal sewer system, you’re only protected if your policy includes the right add-on.

Keep in mind that this optional coverage comes with a payout limit. That’s the maximum amount your insurer will reimburse in the event of damage. It’s critical to choose this limit carefully. Backup-related expenses can escalate fast: think cleanup, disinfection, drying, demolition, rebuilding, replacing damaged belongings, and maybe even temporary relocation costs. You’ll want to consider the value of your basement contents, the likely cost of repairs, and your ability to cover anything not reimbursed. Because let’s face it: when water rises, so does the bill.

A backwater valve is smart—but not enough on its own

A properly installed backwater valve ensures wastewater flows out—and stays out—even when the city sewer system gets overwhelmed. That’s why they’re required in all new residential builds with plumbing fixtures below ground level.

For older homes, it’s not always mandatory, but many insurers now require one to be installed after a backup incident and before they renew your policy. Some Quebec municipalities have also made backwater valves compulsory in all homes, whether new or old.

That said, a valve isn’t your only line of defence for sewer backups. Simple habits can also reduce your risk. Avoid dumping food scraps, grease, or trash into sinks and toilets, as this can clog pipes and increase the odds of a backup.

Finally, if you ever notice dirty water starting to rise in your toilet, tub, or shower, act fast. That’s a red flag. Shut off your home’s main water supply and call a plumber immediately. You could be facing an active sewer backup, and time is of the essence.