Backwater Valve

Sewage in a basement or on a ground floor is a mess. Installing a backwater valve can prevent sewers from backing up and may make you eligible for a rebate.

Sewage Backups Happen

Sewer systems are typically gravity based and flow through to a wastewater treatment plant. When a sudden heavy rainstorm flushes debris into mainline storm sewers and sanitary sewers, sewers can backup into homes and businesses. When these two types of sewer systems are overwhelmed, sewage will back up. Tree roots or grease in a home's sewer lines can also lead to backups.

How a Backwater Valve Helps Prevent Flooding

A mainline backwater valve can help prevent sewage in an overloaded main sewer line from backing up into your basement. Placed directly into the sewer lateral in your basement , the valve automatically closes if sewage backs up from the main sewer.

Before Installing a Backwater Valve and/or Sump Pump

  1. Talk to your municipal government to clarify any local permit requirements.
  2. Find out what type of equipment is recommended by your municipal government.
  3. Check that your foundation drain and eavestrough downspouts are not connected to the weeping tile and sanitary sewer. In the majority of cases, disconnection of a foundation drain will require installation of a sump pit and sump pump.
  4. Hire a licensed plumber to install a mainline backwater valve as well as to acquire the proper building permits. Your municipal government may have a list of pre-approved plumbers.
  5. When eavestroughs are disconnected from the sewer system, they should be drained onto your property in a way that does not direct water towards your neighbours. Contact a plumber and your municipal government for advice on how to properly disconnect downspouts and foundation drains.

Not All Backwater Valves Are Equal

Some types of backwater valves, such as the plug type, are not recommended. While they may prevent water from entering your basement, they allow sewer backup pressure to build beneath your basement floor. This can potentially cause structural damage to your home.

Insurance and Backflow Valves

Depending on where you live and the prevalence of sewer flooding events, your insurer may require you to install a backflow valve. If you have suffered substantial sewer backup damage, the installation of a back water valve may be required to maintain insurance coverage. Some municipalities offer rebates to encourage installation of these preventive devices. For more information on how installing a backwater valve can help with your home insurance premiums, contact your insurance broker or agent.  


Handbook for Reducing Basement Flooding, Institute for Catastrophic Loss Reduction