Basement floor drain backing up: causes, who pays and what to do

The floor drain is the lowest opening in most Ontario homes, so it is where water shows up first when anything downstream is blocked. Water from the washing machine, showers and toilets all leaves through the same main drain. When that drain cannot empty, the water rises to the lowest point it can reach, which is the basement floor. The timing tells you a lot about which side of the property line the problem is on.

Why is my basement floor drain backing up?

What should I do first when the floor drain backs up?

1. Stop using water: no laundry, dishwasher, showers or flushing until the line is clear.
2. Keep people and pets out of standing water. If water is near outlets, the furnace, extension cords or the electrical panel, do not walk into it; call your electricity utility to disconnect power.
3. Call your municipality before a plumber. In Toronto, call 311: Toronto Water sends staff to check whether its sewer and its part of your pipe are draining. In Newmarket, call the Town at 905-895-5193.
4. Find your cleanout, the capped access pipe on the main drain, usually near where the drain leaves the house. Crews and plumbers need it to be working and reachable.
5. Take photos and video of the water and damage, and call your insurer.

Who is responsible for a sewer backup, the city or the homeowner?

Ownership splits at the property line in most Ontario municipalities. The City of Toronto owns the sewer service pipe from the main under the street to the property line, and the homeowner owns it from the property line into the house. When you call 311, Toronto Water checks whether city sewers are draining and inspects the service line with a camera. If the blockage is on the city side, crews clear it; if the city side is clear, the problem is on private property, and the owner hires a licensed plumber.

In Newmarket, homeowners are responsible for unblocking their own sewer lateral, and the Town does not clear blockages on private property. The Town handles the part of the lateral on Town property. If you or your plumber believe the blockage started on the Town side, the Town asks for evidence such as camera footage and the location and type of the blockage before it investigates. Other York Region towns, including Aurora, run their own programs; check your town's sewer page before you pay for work on the street side.

Will a backwater valve stop my floor drain from backing up?

A mainline backwater valve is the device that stops sewage from the municipal sewer flowing back into the house. It sits in the main drain under the basement floor, stays open for normal flow, and closes when water tries to come back in. It does not help with a blockage in your own lateral, because the water then comes from inside the house.

A plug or flapper fitted only in the floor drain protects only that one opening. One RedFlagDeals homeowner had a floor-drain backflow device and still had sewage come up through a toilet and shower, which is what happens when the rest of the basement plumbing is left open. Installing a mainline backwater valve means breaking the basement floor, needs a building permit, and should be done by a licensed plumber. The valve then needs occasional cleaning and inspection.

The City of Toronto's Basement Flooding Protection Subsidy Program pays up to 80 percent of the invoiced cost, to a maximum of $1,600 per backwater valve, for up to two devices, and up to $6,650 per property across all eligible work, for work completed on or after November 12, 2025. Toronto requires a building permit and a City-licensed contractor, and applications are due within two years of the work. Outside Toronto, ask your municipality whether it offers a similar program; Newmarket's sewer blockage page does not list one.

Can I clear a floor drain myself?

You can plunge the lowest fixture or remove the floor drain cover to take out hair and debris you can reach. Renting a drain auger and feeding it down the main is a different job. It can get stuck, it can damage an old clay or cast-iron lateral, and in Newmarket the Town requires the free Sewer Safety Inspection before a sewer lateral is cleared. If water is coming up from the floor drain, the blockage is usually beyond the reach of hand tools anyway.

What does drain cleaning cost on Doyo?

On Doyo, Drain Cleaning is $259.60, the full price with Doyo's fee included. It covers a licensed plumber with a Certificate of Qualification (306A), one drain line cleared, a power auger and a camera where it is needed, and clean-up after. If the camera shows a broken or collapsed pipe, the repair is priced separately as Pipe Repair, by written quote after diagnosis. Doyo checks the plumber's 306A before they are offered plumbing work.