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Dirty water in the basement

Sewer backup in the basement: what to do and who to call

Dirty water rising through the floor drain? Our plumbers respond day and night to a sewer backup: they restore the flow, find the cause and help you protect the basement with a backwater valve. Someone on our team answers right away and tells you what to do in the meantime. Below, you'll also find what to do in the first hour and what the City handles.

Call now (438) 379-2352 Request a quote

A plumber answers day and night · RBQ licence 5881-1431-01 · CMMTQ member · Insured

5.0 out of 5 · 121 Google reviews Rating checked on October 14, 2026 Read the reviews on Google
Dirty water rising through a basement floor drain

Why call us for a sewer backup

A plumber from our team arrives within 60 minutes and knows the steps that follow a backup: 311, your insurer and, if needed, a claim to the City.

5.0 out of 5 · 121 Google reviews

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  • Day and night, holidays included

    Backups often happen during heavy storms. Our plumbers are on call at all times, evenings, weekends and holidays included.

  • Our own plumbers

    The plumber who comes to your home is part of our team: your call is not passed to a subcontractor, even during a storm.

  • A written report for your insurer

    We can give you a written report describing what caused the backup, the document your insurer will ask for.

  • A backwater valve, installed and guaranteed

    We install and replace backwater valves after checking how your drains are connected, and the work is covered by a written warranty on labour and parts.

A plumber answers day and night

Talk to a plumber

(438) 379-2352
  • Price confirmed before we head out
  • Someone on our team answers right away
  • RBQ licence 5881-1431-01
  • 5.0 out of 5 · 121 Google reviews

What to do in the first hour

Safety first. If the water is near outlets, plugged-in appliances or the electrical panel, don’t walk in it or touch anything: switch off the basement circuits at the panel only if you can reach it from a dry spot, otherwise call Hydro-Québec. Sewer water carries bacteria, so wear boots and gloves.

  1. Stop sending water down the drains. No flushing, no laundry, no dishwasher. Every litre that goes into a blocked line comes back up at the lowest point.
  2. Take photos and videos of the water, the walls, damaged belongings and the drain it is coming from, before you move anything. Your insurer will ask for them.
  3. Get what you can off the floor: boxes, electronics, papers.
  4. Make the calls: 311 if you are in Montréal, and a plumber for the private side.

Who is responsible for the sewer connection: the City or the owner?

In Montréal, building owners are responsible for all the sewer connections of their building, up to the point where they join the municipal sewer beneath the street, and the City takes action only on the part under public property. So a backup can start on either side, and that changes who does the work and who pays.

For a backup, the City asks residents to contact 311. If a broken connection is suspected and a repair is requested, the City requires a video inspection by a plumbing company accredited by the CMMTQ and licensed by the RBQ, at the owner’s expense.

Our company holds its RBQ licence and is a CMMTQ member. We work on the private side and can give you a written report for your paperwork.

Why do sewers back up?

Most of the time, water comes back up because the pipe has narrowed on your side or because the public system is overloaded. The causes our plumbers see most often:

  • A clog in the private connection

    Grease, wipes and buildup slowly narrow the pipe, until the smallest extra flow comes back up into the basement.

  • Tree roots

    They work their way in through the joints of older clay pipes and form a net that catches everything.

  • An overloaded municipal sewer

    During heavy rain or snowmelt, the public system can push water back into basements.

  • A missing or dirty valve

    A stuck or dirty backwater valve can’t close when the sewer surges. A sagging or broken pipe has the same effect: water pools at the low point.

How our plumbers deal with a backup

Once the emergency is under control, we look for the cause so the backup doesn’t happen again. Every visit follows the same steps.

  1. A price before we leave. On the phone, we look at the situation with you and the price is confirmed before anyone drives out, with no obligation.
  2. Flow restored. The plumber clears the line through the most suitable access point and checks that the water drains normally.
  3. The cause found. They check the access points, the condition of the backwater valve if there is one, and how the water drains after the line is cleared. When the problem sits further down the connection, a pipe inspection tells a clog apart from a break.
  4. A clear plan. You know whether it is routine maintenance or a repair to plan. You pay once the flow is restored, and the written report is ready for your insurer.

How much does a sewer backup call cost?

It depends on where the blockage is, how easy the line is to reach and what the work involves. A blockage in your own connection, between the house and the property line, is cleared through the cleanout in the basement. Roots or a sagging pipe take more work than a buildup of wipes or grease. If water comes back up because the street sewer is overflowing, the problem is on the City’s side: the plumber explains it and checks the condition of your valve. On the phone we ask the right questions and confirm the price before sending the plumber.

  • The price is confirmed before we head out, with no hidden travel fee.
  • No obligation on your side.
  • Evenings, weekends and holidays included.
  • You pay once the flow is restored.
Get my price by phone · (438) 379-2352

How to prevent a sewer backup

Have a backwater valve installed on the main drain: it closes when water from the municipal sewer surges back. In Montréal, the City notes that for a sewer backup its responsibility is not automatic if you do not have a properly working backwater valve. A valve that is there but clogged doesn’t protect anything: it has to stay accessible, clean and checked.

We install backwater valves and replace valves that no longer seal properly. The plumber first checks how your drains are connected, then shows you how to open and clean the valve. It’s work you can schedule when it suits you, ideally before the heavy-rain season. For other early signs to watch, see our drain cleaning page.

Plumber clearing a floor drain with a powered machine

Documenting the damage for your insurer

After a backup, insurers usually ask for photos, a list of damaged property, invoices for the work and the plumber’s report on the cause. If you believe the City is responsible, note that a claim for material damage must reach it within 15 days of the incident. Keep everything, and photograph what you throw away before it goes.

If the water damaged walls or floors, our page on water leaks and water damage covers the next steps.

Sources

Our process

Here is what happens after you call, day or night.

  1. Step 1

    You call

    We listen to what happened and how serious it is. The price is set on that call, before a plumber is sent. No obligation, and no hidden fees.

  2. Step 2

    We head out

    An RBQ-licensed plumber who is a CMMTQ member leaves for your address. The truck is stocked for the job, so the visit can be handled the first time.

  3. Step 3

    Fixed, and guaranteed

    The work follows RBQ standards. You pay once the problem is resolved, and you leave with a written guarantee on labour and parts.

No-obligation quote

Get your price before we head out

Tell us what you need in a few words. We call you back at the number you give to ask the right questions and confirm the price.

Want to add photos? Use the full form

  • The price is confirmed before we head out
  • No obligation on your part
  • RBQ-licensed company, CMMTQ member
5.0 out of 5 · 121 Google reviews Rating checked on October 14, 2026 Read the reviews on Google

An emergency? Don’t write, call: (438) 379-2352

What our clients say

5.0 out of 5 · 121 Google reviews Rating checked on October 14, 2026 Read the reviews on Google

  • “I had a wonderful experience with this plumber! He was extremely nice, kind, professional, and very respectful. He arrived quickly, worked efficiently, and fixed the issue much faster than I expected. I really appreciated his excellent service and positive attitude. I highly recommend him to anyone looking for a reliable and professional plumber. Thank you so much! 🙏”

    Lena O. · Google

  • “The guys were amazing! Came in quick, same day actually, even on a Sunday. They did a fab job and my sink is working better than ever. Thanks team! 🫶🏻”

    Clari S. · Google

  • “I highly recommend Plomberie Pipemasters. When I called, they arrived promptly and fixed the leak quickly. They were professional and left the area clean and in order.”

    Annabelle H. · Google

Common questions about sewer backups

(438) 379-2352
Why does my basement smell like sewage?

Most often a floor drain or a rarely used trap has dried out and lets sewer gas through. Pour water into the drain to restore the water seal. If the smell comes back quickly, or comes with gurgling or rising water, a blockage or a backwater valve problem is likely and the line should be inspected.

What exactly is a sewer backup?

It is wastewater flowing back into the building instead of draining to the municipal sewer, either because the line is blocked or because the street sewer is overloaded, for example during heavy rain.

Should I call the City or a plumber?

In Montréal, the City asks you to call 311 for a sewer backup. The City only works on the public part of the connection. Inside the building and on the private side, you need a plumber. Doing both is often the best approach.

Can you install a backwater valve in my home?

Yes. We install backwater valves and replace valves that no longer seal properly. The plumber first checks how your drains are connected, then explains where the valve should go and how to maintain it. It's work you can plan, ideally before the heavy-rain season.

Would a backwater valve have prevented it?

A working backwater valve keeps water from the municipal sewer from flowing back into the building when the public system is overloaded. It does not protect against a clog in your own line, and it needs regular cleaning and checks to work properly.

Related services

An emergency right now?

Call: someone on the team answers, looks at the situation with you and gives you the price before anyone drives out.

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