Homeowner guide · Sewer-side defence
Backwater Valve Guide
When heavy rain overloads the municipal sewer, water can try to come back up the drain pipe into your basement. A backwater valve is the device built to stop it.
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- Aurora & York Region
Jump to a section
- How they work
- Valve types
- Cleaning and checks
- Subsidies: check current terms
Quick checklist
Have these on hand
- Bucket and old towels
- Flashlight or headlamp
- Adjustable wrench and channel-lock pliers
- Rubber gloves
Stop and call when
- Water is coming through a ceiling
- A drain is backing up into the basement
- There is a gas odour: get outside before phoning anyone
- A fitting will not loosen without twisting the pipe behind it
How they work
A backwater valve is installed on the main sewer line inside the house, usually under the basement floor near the front wall. Wastewater normally flows out toward the street. When the flow reverses, a flap or gate inside the valve closes and seals the line, keeping sewage from rising through floor drains, toilets and showers in the basement.
The valve sits in an accessible chamber with a removable cover, so it can be inspected and cleaned. A properly installed valve is set level and protected by the cover so nothing falls into it.
Valve types
Two broad designs are common in residential work:
- Normally open: the flap stays open and floats closed when backflow occurs. Water and air move freely in normal use, which helps venting and reduces the chance of solids catching on the gate. Many Ontario municipalities prefer or require this type.
- Normally closed: the gate rests shut and is pushed open by outgoing flow. These are less common in homes and may not be accepted locally.
Some installations add an alarm or clear cover so you can see the flap. The right choice depends on your plumbing layout and local requirements.
Cleaning and checks
Backwater valves need occasional attention. Grease, paper and debris can collect around the flap and stop it seating.
- Remove the access cover and look inside a couple of times a year.
- Check that the flap moves freely and there is no build-up on the seat.
- Clean any debris with gloves and a scraper, following the maker's instructions.
- Make sure the cover goes back on securely.
- Have it checked after any sewer backup event.
If the chamber is under flooring or furniture, keep a clear path to it. A valve you cannot reach is a valve that will not get cleaned.
Subsidies: check current terms
Some municipalities offer subsidies or grants to help homeowners install backwater valves and disconnect downspouts. Program details, eligibility and amounts change, and some require a pre-approval and inspection. Before you book work, contact the Town of Aurora, or your own municipality if your home is in a neighbouring community, and confirm what is currently on offer. Ask what paperwork is needed and whether a permit is required. Most valve installs involve cutting the basement floor and altering the drain, so a plumbing permit is typically needed; read plumbing permits in Aurora.
Our backwater valve installation page covers the process, and backflow prevention explains a related but different device for the water supply. For a whole-home view, see preventing basement flooding.
Aurora customers often ask
Is a permit required for a backwater valve?
In nearly all Ontario municipalities, yes. Installing one alters your drainage and typically requires a plumbing permit and inspection.
Is a backwater valve the same as a backflow preventer?
No. A backwater valve protects your drains from sewer backup. A backflow preventer protects the drinking water supply from contamination.
How often should a backwater valve be cleaned?
Give it a look twice a year or so and clean it when needed. Follow the manufacturer's guidance.