Should a backwater valve be part of a basement waterproofing plan in Ottawa?

A backwater valve and basement waterproofing address different ways water gets into a basement, so whether a valve belongs in your plan depends on which problem you are actually solving.

The City of Ottawa identifies three ways water enters a basement: sewer surcharging (sewage backing up through the drain lateral), groundwater leaking through cracks or joints in walls or floors, and overland water coming in through windows, doors or cracks. A backwater valve is a plumbing device that closes when flow reverses in the building drain, so it addresses the first cause. Waterproofing, drain tile and sump systems address the second. The City's protective plumbing FAQ says these devices will not stop water from entering through cracks in walls, failed foundation drains, poor lot drainage or overflowing eavestroughs.

If your basement flooding comes from groundwater, a backwater valve alone will not fix it. If it comes from sewer surcharging, a membrane or interior drain system will not fix it. If you have had both, or are not certain which is the source, a contractor or licensed plumber needs to look at the house before you decide what to install.

The two are not mutually exclusive: a flood plan for one house can include both, once the contractor or plumber has said which entry points apply.

A few things worth knowing if a valve is part of the conversation:

• The City's Residential Protective Plumbing Program offers rebates on indoor sanitary backwater valves (up to $1,000), storm backwater valves (up to $1,000) and outdoor storm backwater valves (up to $2,500). The City rebates the lesser of the maximum or the actual cost of the work. The work must be complete and the rebate application received within 18 months of the building permit's issue date, following the City's change to that window on July 1, 2026. The City lists the program as currently under review, so check ottawa.ca before relying on it.
• A building permit is required before the valve is installed, with floor plans and the device's location, type, make and model.
• Ontario's Building Code (clause 7.4.6.4) requires a backwater valve in a building drain to be of a normally open design and serve no more than one dwelling unit.
• Plumber is a compulsory trade in Ontario, so ask whether a licensed plumber does or signs off the plumbing part of the installation.

Start by asking a licensed plumber to identify which entry point caused your flooding, because the answer determines whether a backwater valve, waterproofing work, or both belong in your plan.