Basement Flooding

Reduce your Risk of Basement Flooding: General Information


Every home is at risk of basement flooding, even if there has never been a flooding incident. Water in your basement is most likely to occur when there's been a heavy rainfall, snow is melting or we're experiencing a spring thaw. The good news is that you can prevent or at least reduce the chance of this happening.

Protect your basement from flooding

Causes of basement flooding on private property:

There are a number of reasons why basements flood. Flooding can occur:

  •  When stormwater or ground water seeps into the home (drainage failure):
      • A crack or leak in your home's foundation, basement walls, or basement windows or door.
      • Poor lot grading or drainage
      • Failure of the weeping tile system (foundation drains)
      • Failure of a sump pump (in some homes) used to pump weeping tile water.
      • Overflowing eavestroughs
      • Leaking or plugged downspouts
  • From a sewer backup:
      • When waste water from the sanitary system or a combination of waste water and stormwater from the combined sewer system back up into the property, usually through fixtures tied to the sanitary sewer lateral, including the floor drain, toilets, sinks, showers and laundry fixtures located in the basement.
      • A sewer backup can result from a blocked connection between your home and the main sewer in the street, a sewer main backup or when the sewer system becomes overwhelmed with stormwater.

Understanding Toronto's sewer system

There are three types of sewers in Toronto:

  • Sanitary sewer: The sanitary sewer, which carries wastewater (sewage), is connected to a home's plumbing (toilets, sinks, laundry, floor drain etc.) and leads to a wastewater treatment
  • Storm sewer: The storm sewer collects stormwater from catchbasins (street drains), connected downspouts, weeping tiles (in many areas of the city) and carries these flows into nearby watercourses, and ultimately into Lake Ontario.
  • Combined sewer: In older parts of the city, stormwater and sewage are collected in the same pipe known as a combined sewer. During normal weather conditions, all the wastewater in the combined sewer is treated at the wastewater treatment plant.

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What the City is doing to stop flooding

The City of Toronto takes flooding incidents seriously and is taking steps to stop the overloading of the sewer system and reduce basement flooding. Actions taken include:

  • Mandatory Downspout Disconnection Program requires homeowners to disconnect their home's downspout from the City's sewer system, where feasible, to help reduce sewer flows. (City of Toronto Municipal Code, Chapter 681, Sewers)
  • Basement Flooding Protection Subsidy Program provides up to $3,400 to owners of single-family, duplex and triplex residential properties to install flood protection devices, including a backwater valve, a sump pump, and disconnecting external weeping tiles from the sewer system (by severing and capping connected pipes.)
  • Work is underway across Toronto to make improvements to local sewer systems and overland drainage. Read more about the Basement Flooding Protection Program.
  • Regular inspection, cleaning and maintenance of the City's sewer system.

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Stop the flood before it starts

Here are some steps you can take to reduce the likelihood of basement flooding.

What you can do outside the house

  • Seal cracks or openings in walls, floors, windows and foundations, and seal all window wells.
  • Clear eavestroughs and downspouts of leaves and other debris that prevent proper drainage.
  • Disconnect your downspouts from the sewer system, where feasible (without negatively affecting neighbouring properties or creating an area where water will pool on a sidewalk or driveway) .
  • Make sure your disconnected downspouts are draining properly, ideally two metres (six and a half feet) from your foundation's walls.
  • Ensure the grading around your home slopes away from the foundation wall to help drain water away from your home (without negatively affecting neighbouring properties).
  • Increase the green space around your home with native plants and shrubs and install porous pavement to help absorb rainwater and melted snow.
  • Repair/replace damaged weeping tile systems.
  • Clear debris from roadside catchbasins (grates) to help water enter the stormsewer. (If it is safe to do so.)
  • Ensure drainage swales (shallow ditch) between properties are maintained and clear of obstructions.


What you can do inside the house

  • Ensure that your plumbing and drainage systems are in good working condition. Homeowners are responsible for the plumbing from the property line to inside the home.
  • Part of reducing the risk of basement floods is to understand how your plumbing and foundation drainage systems work and how to maintain them. Every home is different and homes over time have been built with different building practices and building codes. Some of what you should know about your home, includes:
    • Know the location and condition of your sewer lateral (the pipe that connects the plumbing in your home to the main line on the street).
    • Find out if you have a storm sewer lateral (pipe) and if so the location and condition of it.
    • Find out if you have a backwater valve or sump pump, and if so, how to maintain them. Understand what is needed to keep a sump pump operational during power outages.
    • Find out if you have weeping tiles and if so, their condition and where they are connected. (A weeping tile is a perforated pipe that runs around the perimeter of your foundation to intercept groundwater. The weeping tile gives the groundwater a place to go. Where it goes depends on the type of foundation drainage system your home has.)

To understand some of these elements of your home, you may want to hire a licensed plumber who can conduct specialized testing or inspection, often through video camera inspection.

  • Once you understand your plumbing and drainage systems, you also have to maintain them. 
    • Fix cracks, blockages or other condition problems.
    • Avoiding creating clogs:
      • Toilets are not for trash. Do not flush down the toilet items such as dental floss, personal care products (including "flushable" wipes), condoms, tampons, razor blades or anything which can block the sanitary pipe.
      • Never pour any fats, oils, and grease down the drain.
  • Hire a City-licensed and qualified plumber to install a backwater valve and a properly-sized sump pump and piping. Ensure the proper and regular maintenance of basement flooding devices in your home.Sump pumps need power to operate, so consider installing a back-up power source.
  • Seal cracks or openings in walls, floors, windows and foundations, and seal all window wells.

Click picture for larger image

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 Information on backwater valves and sump pumps

Consider hiring a City-licensed plumbing contractor to conduct a detailed plumbing investigation to help assess and recommend options to reduce flooding. It is advisable to get estimates before going ahead with any work.

The City offers a financial subsidy of up to $3,400 to homeowners of single-family, duplex or tripleplex residential homes to install flood protection devices through the Basement Flooding Protection Subsidy Program. For details, go to: Basement flooding.

A licensed plumbing contractor can assist to:

  • Install a backwater valve (see diagram below) on your sanitary and/or storm sewer line to prevent water from backing up into your basement. Backwater valves need to be installed properly and regularly inspected and maintained. Find out which type of backwater valves the City's subsidy program will cover. For details, go to: Basement Flooding
    Install a backwater valve diagram
    Important: Backwater valves are designed to close the sewer line and prevent water from entering your home. When the valve is closed you should not use any plumbing fixtures, such as toilet, sink, dishwasher, washing machine, etc., because water will not drain through the sanitary line and will backup into your home.


  • Install a properly-sized sump pump, (see diagram below) to help pump out water collected by the weeping tile system to an area outside. Make sure the sump pump empties onto a permeable surface at least 2 meters from the foundation wall. Sump pumps can lose power during severe storms, so you may wish to consider a battery back-up. 
    Install a properly-sized sump pump diagram
  • Backwater valves and sump pumps need to be inspected and maintained to ensure optimal performance.
  • Some work may need a building permit. For information on how to obtain permits, call 311 or visit Toronto Building

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What to do when your basement has flooded

  1. If you experience basement flooding, contact 311 immediately (24 hours a day, seven days a week).   City staff will inspect the problem, assess the flooding and attempt to determine the source(s) of the flooding.  Dial 311 on your phone or visit enter a self-service request.
    • Don't use toilets and sinks unless it is absolutely necessary until the issue has been resolved. (Any water sent down the drain may end up in your basement.)
  2. Call your insurance company as soon as possible and report property damage caused by the flooding:
    • Take photos of damage caused by flooding for your insurance claim.
    • Keep receipts from emergency repair work or clean-ups done to prevent or reduce further damage.
    • If the flooding is a result of a blocked drain pipe, leaking foundation walls or poor lot drainage on your property, then you are responsible for repairs and any subsequent damage caused by flooding. Contact your insurance company to discuss coverage.
    • You may submit a claim in writing with your name, telephone number, home address, date, location and details of the incident and send it to:
      City Clerk's Office, City of Toronto
      City Hall, 100 Queen St. W.
      Toronto, ON  M5H 2N2
      Or fax: 416-392-2980 or e-mail
    Your claim will be forwarded to the City's insurance adjustors for evaluation. A letter of acknowledgement will be sent to you.
  3. Be mindful of health and safety when cleaning up your flooded basement. Exposure to contaminants carried by flood water or sewer back-ups into basements can be dangerous. Homeowners may be exposed to waterborne diseases, corrosive cleaning agents and irritants found in leftover sludge from a flooded basement. Electrical accidents may occur because of contact with water and electricity.
    • Consider hiring a professional cleaning company familiar with cleaning sewage contaminated basements.
    • Keep children and pets out of the affected area until cleanup has been completed.
    • Dress appropriately – wear overalls, gloves, protective eyeglasses, rubber boots and a mask.
    • Open windows to let fresh air in.
    • Stay away from electrical equipment. Have a qualified electrician assess the situation, if uncertain of potential electrical hazards.
    • If you can, shut off the electrical power. (Note: would affect the operation of a sump pump or sewage ejector).
    • Water could extinguish a pilot light on a gas appliance. If you detect gas, leave the house immediately and contact the gas company.
    • Minor debris can be put out for regular garbage pick-up (See your Garbage and Recycling Collection Calendar for information).
    • Discard all contaminated items that cannot be washed and disinfected, (such as, mattresses, carpeting, carpet padding, rugs, upholstered furniture, cosmetics, plush toys, baby toys, pillows, foam-rubber items, books, wall coverings, and most paper products).
    • Wash all surfaces with hot water and liquid detergent, rinse and thoroughly dry and ventilate the area. Use de-humidifier and fans if necessary.
    • Sanitize walls and floors using a solution of household bleach (mix 1 cup bleach with 5 gallons of water). Never mix bleach with ammonia or other cleaning products. For more details, visit the Centre for Disease Control and Prevention's website.
    • Remove and discard drywall and insulation that has been contaminated with sewage or flood waters.
    • Wash all clothes worn during the cleanup in hot water (check manufacturer's washing instructions) and detergent. These clothes should be washed separately from uncontaminated clothes and linens.
    • Throw out canned foods, home-prepared food in jars, meats and dairy products and any packaged foods that may have been affected by the flood waters – check for damaged packaging, leaks, and corrosion at seams and joints of cans.
    • If your freezer's power is off, move the frozen food to another freezer or throw it out if you can't keep it frozen.
    • If in doubt, throw it out. Do not consume potentially contaminated food. For more information visit Toronto Public Health for information on food safety after a power outage.
    • Visit Toronto Public Health for more information on cleaning up after a flood.

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Keep your plumbing clear

Avoid creating blockages in your plumbing and the City's sanitary sewers:

  • Dispose of small amounts of cooking oil and grease in your green bin (making sure there's material to absorb it). Never pour oil or grease down the kitchen sink or into the toilet. Grease can build up and cause blockages in the City's sanitary sewer pipes, which can cause basement flooding.
  • Toilets are not for food, trash, dental floss, Q-tips, or other personal care objects, including "flushable wipes". These should be disposed of in the appropriate bin.

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