Backwater valves explained: does your Lower Mainland home need one?

How a backwater valve works

It's a one-way valve installed on your home's main sewer line. In normal use, a flap inside stays open and wastewater flows out to the street. If sewage starts flowing the wrong way, the flap closes and blocks it from entering your home.

Homes that benefit most

• Homes with a finished basement, or a basement bathroom, laundry or floor drain.
• Homes where the basement fixtures sit lower than the street.
• Homes in low-lying, flat areas, which describes much of Richmond and parts of Delta and Surrey.
• Homes on streets that have had sewer backups before. Ask your neighbours.

One thing many owners don't know

While the valve is closed, water from your own house can't drain out either. During a severe storm, hold off on showers, laundry and the dishwasher until the heavy rain passes. Otherwise your own wastewater can back up behind the closed valve.

Do you already have one?

Look for a round or rectangular access cover in your basement floor, often near the floor drain or where the sewer line leaves the house. Some have a clear lid so you can see the flap. If you're not sure, a plumber can confirm it in a short visit, and a camera inspection will show the condition of the line as well.

Looking after it

A backwater valve only works if the flap can move freely. Grease, debris and wipes can jam it open. Have it checked and cleaned about once a year, ideally before the rainy season, and never flush wipes, even the ones labelled flushable.

Installing one

Installation means cutting into the main sewer line, usually under the basement floor, so it's a job for a licensed plumber and it normally needs a permit from your city. It's also worth asking your home insurer whether a backwater valve affects your sewer backup coverage, since some insurers ask about them.