Guide: flood defence
Backwater Valves: How They Work and Upkeep
A backwater valve is a simple device with an important job. Here is how it works, what it guards against and the twice-yearly check.
- Find the access cover in the basement floor, usually near the front wall.
- Remove the cover and look inside with a flashlight.
- Check the flap moves freely and closes fully.
- Remove any debris caught in the valve.
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The basic idea
Your main sewer line carries waste from the house to the city sewer. During heavy storms, the city sewer can fill and push water back toward your house. A backwater valve sits in your main drain with a flap that lets water flow out but closes when water tries to come back.
Types of valves
- Normally open valves stay open for flow and close only during a backup. These are the common type for mainline use in Toronto.
- Normally closed valves stay shut and open under flow. They are used in some situations but can restrict venting.
Checking the valve
- Find the access cover in the basement floor, usually near the front wall.
- Remove the cover and look inside with a flashlight.
- Check the flap moves freely and closes fully.
- Remove any debris caught in the valve.
- Check the seal on the access cover and replace it.
Do this in spring and fall. If the valve is hard to reach or you are unsure, call us.
During a storm
While the flap is sealed, nothing you flush or drain upstairs can get out to the street either. Limit water use during heavy rain: skip laundry, long showers and the dishwasher until the storm passes. See backwater valve installation and the subsidy guide.