Sewer backups and basement flooding

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Causes of sewer backups and flooding

The sanitary sewer system collects wastewater from your home through a pipe called a sanitary lateral. This lateral carries wastewater from toilets, washing machines, dishwashers, showers and sinks to the sewer main, which carries wastewater from other homes and businesses to the City's wastewater treatment facility.

Foundation drains collect groundwater from around the foundation of your home and are usually connected to the storm sewer by a storm lateral. In some older homes, these drains are connected to the sanitary or combined sewer by a sanitary lateral, or are not present. Water from rainfall events and snow melts are also collected by storm sewers and directed to nearby watercourses or stormwater management ponds.

While the City regularly cleans, inspects and repairs the sanitary and storm sewer systems, unanticipated problems can occasionally occur, causing increased water levels in the sewer (or surcharging).

Flood prevention diagram

Backups and flooding can occur as a result of:

Blockage of the lateral

If the lateral from your home becomes blocked, sewage from inside your home may back up into the basement. The blockage may be due to:

  • Accumulation of grease, paper, kitchen waste or other foreign objects
  • Presence of tree roots (private or City-owned trees)
  • Collapse, misalignment or other structural defects of the lateral

Surcharging of the City’s sewer main

If the sewer main, generally located under the street, is blocked or damaged, sewage may enter your home due to increased water level or surcharging in the City’s sewer system. Sewer surcharging may be due to:

  • Collapse or other structural defects.
  • Blockage by waste and debris.
  • Heavy rainstorms or spring runoff.
  • Construction activities in the area.

Spring runoff

Melting snow and ice can leak through cracks or joints in your basement walls or floor.

River flooding

River flooding sometimes occurs in some areas of the city. Each spring the City clears ice from the Rideau River to prevent serious flooding.

To find out if you live in Ottawa's 1-in-100 year flood plain, consult the City's interactive map.

Alternate types of sewer systems

In some older homes, foundation drains are connected to the sanitary or combined sewer by a sanitary lateral, or are not present. Basement flooding caused by sewer backups can originate from different sources depending on the type of sewer system in your area.

Please note: New buildings (or “infill”) in older areas of the city may have more modern sewer connections than described below.

Partially separated area

  • Older buildings with foundation drains connected to the sanitary sewer.
  • Storm sewers only have a street's catch basins connected.
  • Basement flooding risk is generally from the sanitary sewer.

Partially separated area (former combined sewer area)

  • Older buildings with no foundation drains.
  • Catch basins are connected to the storm sewer.
  • Basement flooding risk is generally from the sanitary sewer.

Combined sewer area

  • Older buildings with no foundation drains present.
  • No storm sewer is present.
  • All sanitary laterals, foundation drains and catch basins connected to one combined sewer.
  • Basement flooding risk is generally from the combined sewer.

Responsibility for sewer laterals

  • The City is responsible for the portion of the sanitary and storm sewer laterals from the property line to the street.
  • The homeowner is responsible for the portion of the sanitary and storm sewer laterals from the property line to the home.
  • There may also be shared responsibility if a lateral requiring repair or replacement crosses the property line.

Tips to prevent basement flooding

Residents can help prevent basement flooding with a few simple changes around the home:

  • Seal window wells and cracks in floors, walls and the foundation.
  • Slope ground away from the foundation to allow rainwater to flow away from the home.
  • Direct downspouts from eaves troughs away from the foundation (minimum of 1.2 metres) or to a rain barrel.
  • Disconnect downspouts from the sewer system or foundation drains.
  • Ensure foundation drains direct water to the storm sewer or sump pump. Foundation drains should not be connected to the sanitary sewer.
  • Ensure the sump pump is connected to the storm sewer or discharges to the ground at least 1.2 metres from the foundation.
  • Install protective plumbing devices, such as backwater valves which protect against surcharging in City sewers. The City’s Residential Protective Plumbing Program offer rebates to qualified homeowners.
  • Maintain existing protective plumbing devices according to the manufacturer’s instructions. A protective plumbing device should be maintained periodically or before a forecasted heavy rainfall to ensure it is free of debris, functioning properly and that cleanout caps and access covers are firmly secured.
    • In older homes, especially those with cast iron pipes, additional maintenance may be required, as rust can accumulate at the hinge and prevent proper closure of the backwater valve during a surcharge event.
    • For more tips on backwater valve maintenance, refer to a video on Backwater Valve Maintenance from the Institute for Catastrophic Loss Reduction.

For more tips on preventing basement flooding, refer to the Handbook for Reducing Basement Flooding from the Institute for Catastrophic Loss Reduction.

What to do if your basement has flooded

Recommended homeowner response to basement flooding:

  1. Check the toilets and sinks for blockages.
  2. Wearing appropriate protective clothing, clear any blockages to ensure proper flow.
  3. If this does not resolve the issue, call 3-1-1. The City has expert staff on duty at all times who will respond as soon as possible to these situations. If requesting City assistance, ensure someone 18 years or older is at home to meet City staff.
  4. Locate the sewer clean-out caps. Do NOT attempt to open. Clean-out caps are usually located in the basement floor at the front of the home (near the water meter). Ensure an area at least one meter on all sides of the clean-out is free from obstructions (boxes, furniture) to provide access to City staff.
  5. Avoid using fixtures and appliances which require water, until after the issue has been resolved, as any water sent down the drain may end up in your basement.


Do NOT enter the flooded area until a qualified professional has determined it is safe to enter.


If the flood water level is threatening any gas-fired equipment such as a furnace, hot water heater or stove, contact Enbridge Gas.


If the flood water level has reached any plug, electrical outlet, extension cord or electrical appliance such as a baseboard heater, contact Hydro Ottawa.

More information on flood safety can be found from the Electrical Safety Authority.

Bacteria or viruses

Basement flood water may contain sewage from the sanitary sewer. Flood water contaminated with sewage may contain bacteria and viruses which can affect your health and the health of your family. Be sure to wear protective clothing such as rubber boots, gloves, safety glasses and a facemask, and wash thoroughly after any contact with flood water or items which may have been in contact with flood water.

Flooding and your health: What you need to know

The following links provide information on preparing for a potential flood; protecting yourself and your family during a flood; and restoring your home after a flood. 

For more information on cleaning, disinfecting, mould and re-entering your home, refer to the Government of Canada – Get Prepared or Centers for Disease Control and Prevention.

Contacting your insurance company

Your insurance company will be able to advise you regarding standard clean-up and claims procedures, along with contractors to contact. Generally,

  • Understand your coverage and what type(s) of flooding damage are covered.
  • Photograph and document damaged items or items which will need to be replaced.
  • Retain receipts for any emergency and repair work, along with replacement items.

For more information on home insurance, visit the Insurance Bureau of Canada website. 

City response to basement flooding

  1. City staff will inspect the sewer main near your home to determine whether or not it is functioning normally. If there is a problem, it will be fixed as soon as possible.
  2. If the problem is not related to the sewer main, City staff can help you identify the problem, if resources are available.
  3. If the problem is in the home’s drain system, the homeowner will be advised to contact a plumber.
  4. If the problem is related to either the sanitary or storm lateral, repairs may be the homeowner's responsibility, City's responsibility, or a shared responsibility. Responsibility can only be determined after City staff have reviewed all of the available information.

Preventative Maintenance Program

The City maintains a list of properties confirmed to have experienced a sewer backup caused by City-owned tree roots or structural defects on the City-owned portion of the sewer that cannot readily be repaired.

As part of its Preventative Maintenance Program, the City offers a sewer maintenance service annually (or as otherwise modified) to these impacted properties to ensure the proper function of the sewer and help prevent sewer backups.

For further information, please contact 3-1-1.

Responsibility for the repair costs

The cause and location of the blockage generally determines who is responsible for the cost of removing the blockage or repairing the lateral. Generally, lateral blockages are the responsibility of the homeowner, unless the blockage is due to City-owned tree roots or the damaged portion is on City property. For more information on repair costs and responsibility for those costs, refer to the Sewer Connection By-law, as amended.

If the flooding is due to a blockage on the private portion, a contractor must be contacted. As a homeowner, there is the option to select a contractor of your choice, or the City's contractor. Work not related to removal of a blockage such as repair, relining and replacement are billed directly by the contractor to the homeowner.

If, during the course of the repair work, it is determined that the blockage is located on City property, the homeowner will not be charged for the repair work. If payment has already been made for any work, the homeowner will be reimbursed. The reimbursement amount will be up to the amount typically paid by the City to its contractor for the same service. Requests for reimbursement should be directed to the City's Claims Unit.

In some cases, repair costs may be shared between the City and the homeowner.

Making a claim

Homeowners who have incurred damage to their home or its contents should contact their insurance company for assistance. Typically, your insurance company will submit a claim to the City for investigation/response on your behalf. Claims can be submitted to the City’s Claims Unit.

For more information, please contact our general claims line at 613-580-2655 or by email at

Residential Protective Plumbing Program

The Residential Protective Plumbing Program (RPPP) provides financial assistance to qualified City of Ottawa property owners for the installation of protective plumbing devices, such as sump pumps and storm and sanitary backwater valves to prevent water and sewage from flooding homes as a result of increased water level (surcharging) in the City’s sewer system.

Who is eligible for the program?

To be eligible for the Residential Protective Plumbing Program, the following must be satisfied:


Step 1: Submit Part 1 of Application

Download Part 1 of the application.

Discuss device options with a licensed plumber. Some backwater valves have been specifically designed and approved for retrofit installations to address potential issues such as pipe slope (drainage) and space limitations.

Ensure your completed application is signed and includes the following documentation:

  • Proof of ownership (copy of deed, land transfer or property tax bill), and

The following documents prepared by a licensed plumber:

  • Detailed listing of proposed work (included on application form)
  • Quote for the proposed work
  • Detailed diagram showing existing and proposed work (included on application form)

Applications can be sent via e-mail or mail to the Residential Protective Plumbing Program at or

Residential Protective Plumbing Program
Infrastructure and Water Services Department
City of Ottawa
951 Clyde Avenue
Ottawa, ON K1Z 5A6

Condominium Associations

To proceed with a Residential Protective Plumbing Program application, Condominium Associations must first obtain, in writing, permission from each property owner to act on their behalf.

Download the Homeowner Authorization form. The completed Homeowner Authorization forms should be submitted with the Part 1 Application form.

Step 2: Part 1 Application Review

The City will review your application and will contact you regarding the status of your application, next steps and assigned RPPP file number. Please refer to your RPPP file number when contacting the City regarding your application.

Step 3: CCTV Inspection

Once the application is approved, contact your contractor to arrange for a Closed-Circuit Television CCTV Inspection. The CCTV inspection reviews the sewer lateral from inside the home to the street (main City sewer).

The CCTV inspection and report must meet the City’s CCTV requirements for format, reporting and equipment. The contractor must submit an electronic copy of the CCTV inspection and the inspection report via DVD or to the City service provider’s FTP site.

Once complete, the City or its service provider will contact the applicant to arrange for a site visit.

Step 4: Site Visit

A site visit is required to confirm the protective plumbing work required. This may involve taking measurements and photographs of the existing plumbing. The site visit is free of charge.

NOTE: More than one site visit may be required.

Step 5: Site Visit Review

Once the site visit is complete, you will be contacted to confirm the status of the proposed work and next steps. To avoid unnecessary expenses, a Site Visit Review should be received by the applicant prior to applying for a building permit and undertaking any of the proposed work.

Step 6: Installation

Contact your contractor to arrange for the installation of the approved protective plumbing devices. The backwater valve and its installation must meet the current requirements of the Ontario Building Code, the current City of Ottawa By-laws, Sewer Design Guidelines and Standard Tender documents for Unit Price Contracts.

The applicant or the contractor must obtain a building permit prior to commencing the proposed work, and must arrange for inspections by the City’s Building Code Services Branch. The Building Inspector will need to review your project at several stages during construction – an inspection prior to covering underground plumbing, and a final inspection after the floor has been reinstated.

The building permit application must include copy of the approved Part 1 Application and Site Visit Review.

Sewer Design Guidelines

For more information on the Sewer Design Guidelines or to order a copy, please email the City of Ottawa at Fees do apply.

Note: The Sewer Design Guidelines contain applicable information regarding backwater valve installation, including but not limited to the following sections:

  • 4.4.5 – Sanitary Backwater Valves 
  • 5.7.5 - Service Connection Hydraulics
  • 5.7.7 – Storm Backwater Valves
Standard Tender documents for Unit Price Contracts

For more information on the City of Ottawa Standard Tender documents for Unit Price Contracts or to order a copy free of charge, please email the City of Ottawa at

Note: The City of Ottawa Standard Tender documents for Unit Price Contracts contain applicable drawings and material specifications, including but not limited to the following drawings:

  • S14 – Foundation Drain Backwater Valve Installation
  • S14.1 – Sanitary Backwater Valve Installation Type 1
  • S14.2 – Sanitary Backwater Valve Installation Type 2
  • S16 – Exterior Foundation Drain Backwater Valve Exterior Retrofit Applications (Exception Basis Only);
  • S18 – Typical Depressed Driveway Backwater Valve and Standpipe Detail
  • MS-22.15 - Approved Sewer and Miscellaneous Products Listing (S18.2-1 and S18.2-2).

Step 7: Submit Part 2 of Application

Download Part 2 of the application or obtain a form from your nearest City of Ottawa Client Service Centre.

Ensure your completed application is signed and includes the following documentation:

  • Copy of Building Permit, including receipt(s)
  • Original contractor invoice marked paid in full
  • Copy of Building Code Services inspection report

Prior to the expiration of the one-year deadline (as indicated on the initial approval), you must complete Part 2 Application and submit to the Residential Protective Plumbing Program.

Step 8: Part 2 Application Review and Rebate Processing

The City will review the application and notify the applicant(s) of the status of the rebate. Processing time depends on the volume of applications received. Once approved, a rebate cheque will be issued and mailed to the applicant(s) within eight to 10 weeks.

Application forms

Rebate payment and limits

How much are the rebates?

Item Maximum Rebate Amount
Permit $80
Closed-circuit television video (CCTV) – Sanitary $100
Closed-circuit television video (CCTV) – Storm $100
Indoor sanitary backwater valve only $700
Indoor storm backwater valve only $500
Indoor sanitary and storm backwater valves $1,000
Outdoor storm backwater valve only $1,750
Sump with battery backup power (high gradient or flat roof) $1,250

The City will rebate up to a maximum of each of the individual rebates available at the time of the submission of Part 1 of the application form. Should the cost of the work be less than the amount of the available rebate, the City shall rebate the lesser of the two amounts.

Prior application(s) specific to the property, including those by previous owners, may limit eligibility for specific rebates.

Are there limits to the rebate availability?

Funding is limited. Applications will be processed on a first come, first served basis. If an application is not fully processed due to insufficient funds, the applicant(s) will be notified and the application will be closed. Applicants may submit a new application once funding becomes available.

Can I withdraw from the program?

The RPPP is a voluntary program and you may withdraw at any time.

Protective plumbing: Frequently asked questions

What is protective plumbing?

Protective plumbing prevents water and sewage from entering your home during a backup. These methods can range from installing a sump pump and changing the footing drains around your foundation to installing an approved backwater valve on the sewer pipes connecting your sanitary sewer to the City sewer system.

Function of protective plumbing in a sewer system

What is a sewer lateral?

A sewer lateral is the pipe that connects your home or business to the main sewer in the street. The property owner is responsible for the portion from the property line to the home or business. The City is responsible for the portion from the property line to the main sewer.

How does a sewer backup occur?

Excess rain or snowmelt or a blockage in the sewer system can cause an increase in water level or surcharge. A backup occurs when the increased water level (surcharge) pushes water backwards through the service lateral into the home through floor drains, sinks and toilets.

How can water enter my home?

Identifying the locations where water may enter the home

How do I know if I have a backwater valve installed on my property?

Backwater valves were mandatory in new homes after 2004 (stormwater) and 2012 (sanitary), but some older homes have had them installed retroactively.

If you are unsure of if you have a valve installed on your property, check between the last branch of your sewer line and where the pipe exits your foundation. It may look like a Y-shaped (wye) fitting with the wye branch plugged and pointing upward. If it’s in your yard, it is most likely buried and could be several feet deep.

A backwater valve located in the floor

Why do I hear an alarm near the backwater valve?

An alarm may be added to a backwater valve to alert you that the valve has been engaged and is restricting flow back toward your basement. When you hear the alarm and when you see that the valve is engaged, it means that the backwater valve is working as it should. Do not shower, flush toilets or wash clothing until the system has returned to routine functioning, as additional water will not flow out of the residence when the valve is engaged. You can resume routine use when the alarm and the backwater valve are no longer engaged.

Do I have to maintain my protective plumbing devices?

Yes, the property owner is responsible for maintaining protective plumbing devices according to the manufacturer’s direction. A protective plumbing device should be maintained periodically or before a forecasted heavy rainfall to ensure it is free of debris, functioning properly, and that cleanout caps and access covers are firmly secured. If you are unsure about the condition of the valve or are not able to complete the required maintenance, a licensed plumber can perform an inspection.

For more tips on backwater valve maintenance, refer to a video on Backwater Valve Maintenance from the Institute for Catastrophic Loss Reduction.

Will protective plumbing keep water out of my basement?

If properly installed and maintained, protective plumbing devices will prevent water and wastewater from a surcharging event from entering the home.

Protective plumbing devices will not stop water from entering through:

  • Cracks in walls or window wells,
  • Failed foundation drains or sump pumps,
  • Overflowing eaves troughs and plugged downspouts,
  • Poor foundation drainage,
  • Poor lot drainage, or
  • Water sources inside the house.

Where can I find further resources on protective plumbing?

Contact information

For more information on the Residential Protective Plumbing Program, please contact the City of Ottawa at 3-1-1 or by email at or by mail at:

Residential Protective Plumbing Program
Infrastructure and Water Services Department
City of Ottawa
951 Clyde Avenue
Ottawa, ON K1Z 5A6

Residential grants for sewer backups

Residents affected by flooding three or more times could be eligible for a grant of up to $1,000 under the Residential Compassionate Grant policy for sewer backups.

Apply for a Residential Compassionate Grant

To qualify, the resident (property owner or tenant) must satisfy the following conditions:

  • Proof of three or more sewer backups during a 15-year period that are related to sewer surcharging as a result of significant rainfall
  • Owned or rented the home during all three backups
  • Experienced at least $1,000 of damage during the most recent backup
  • Property owners must have their property taxes paid in full
  • Sewer backups must be reported to the City within four months of taking place

All backups that occur after September 1, 2009 must be reported to the City within four months of the event. You must submit your application within four months of the third backup.

For additional information regarding the Residential Compassionate Grant Program, contact:

Residential Compassionate Grant Program
City of Ottawa
Infrastructure and Water Services Department
951 Clyde Avenue
Ottawa ON K1Z 5A6
Tel: 3-1-1
Fax: 613-728-6928
TTY: 613-580-2401