Backwater Valve Installation in Markham
If sewage has ever come up through your basement floor drain, or your insurer or a neighbour's flood has you worried, we do backwater valve installation in Markham with the permit, the City inspection and the rebate paperwork included. The City of Markham pays back up to $1,750 for an indoor valve, and we price the job in writing so you know your cost after the rebate before we cut the floor.
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Indoor mainline backwater valve: $2,200 to $4,000 installed with permit and inspection. Markham rebate: up to $1,750 indoor, $2,000 outdoor, if the City approves it first. Typical out-of-pocket after the rebate: about $450 to $2,250. One to two days on site.
placeholder imageHow the job goes
We start with a camera through your main line to find the right spot and check the pipe is sound enough to take a valve. Then the City steps come first: if you want the rebate, the City has to approve the work before we start, and a building permit is required either way. On install day we saw-cut the basement floor at the main drain, dig down to the line, cut in a mainline backwater valve with an access box at floor level, and restore the concrete. A City building inspector checks it before the floor is closed. Most installs take one to two days.
| Situation | What is included | Typical range |
|---|---|---|
| Indoor mainline backwater valve, unfinished basement | Saw-cut, dig, valve, access box, concrete, permit, inspection | $2,200 to $3,000 |
| Indoor valve, finished basement | As above, plus moving flooring and trim around the cut | $3,000 to $4,000 |
| After the City rebate (indoor) | Rebate up to $1,750, paid to you after inspection | About $450 to $2,250 |
Prices before HST. Rebate subject to City approval before work. Last checked: CONFIRM: month and year the prices were last checked, e.g. October 2026.
The Markham rebate, in short
The City of Markham's Private Plumbing Protection Rebate pays back up to $1,750 for an indoor backwater valve and $2,000 for an outdoor one. Your property needs to be in a known flood-prone area or able to show flood risk, your downspouts must be disconnected from the sewer, you need City pre-approval and a building permit, and you cannot have outstanding work orders or fees with the City. The building permit has to be issued by April 30, 2027 and the rebate application filed by July 31, 2027. The full step list is on our Markham rebate page.
Watch for calls claiming to be from the City: the City of Markham says it does not phone homeowners to sell flood protection installs.
Who needs one
Any house with a basement floor drain connected to the City sewer is exposed when that sewer surcharges in a storm. The risk is highest in the neighbourhoods on older drainage: Markham Village, Unionville and Thornhill, where the City's own flood studies focus, and anywhere a basement has already backed up once. If your weeping tile still drains into the sanitary sewer, pair the valve with a sump pump and weeping tile disconnection, because the valve alone will hold your foundation water in the house when it closes.
Common questions
What does a backwater valve actually do?
It is a one-way flap in your main sewer line. Wastewater leaves the house normally; if the city sewer surcharges in a storm and tries to flow back, the flap closes and keeps it out of your basement.
Is a backwater valve the same as a backflow preventer?
No. A backflow preventer protects the drinking water supply from contamination and is covered by Markham's Backflow Prevention By-law. A backwater valve protects your basement from sewage. Different device, different pipe.
Can I use water while the valve is closed?
Not much. When the flap is shut, water you run inside has nowhere to go. During a big storm, hold off on laundry, dishwashers and long showers until the sewer recovers.
Does it need maintenance?
Yes. Open the access cover once or twice a year, check the flap moves freely and clear any debris. It takes five minutes and we show you how on the day.
Do I need one for a basement apartment?
Markham's Secondary Suites Guide says that in flood-prone zones you need backwater valves for each dwelling unit. If you are registering a second suite, ask us before the inspector does.