Back water valves may help with sewer water backing up into the house and possibly causing water related damages in the basement. They activate when water reverses and tries to flow into the house.
Backwater valves should be installed by a licensed plumber and require a building permit to be installed. They also need to be maintained and regularly inspected according to product specifications.
The City of Toronto offers up to $1250 in rebates to offset the cost of a backwater valve under the Basement Flooding Protection Subsidy Program. Other municipalities may have there own programs such as Halton Region, Region of Peel and City of Vaughan.
It’s also very important the backwater valve is maintained on a regular basis. Cleaning the inside of the unit is important so nothing blocks the flap from closing. If you have no idea what to do, then you might want to hire a qualified person to assist.
Here are a couple of videos for you to view, many more are on YouTube.