How Much Does It Really Cost to Install a Backwater Valve in London, ON? (2026 Pricing)

If you are tired of worrying every time the Thames Valley region gets hit with a heavy storm, installing a backwater valve (also commonly referred to as a sewer check valve or backflow preventer) is the smartest investment you can make for your home. But for most London homeowners, the first question is always: What is the true installation cost?

The good news? Thanks to the City of London Basement Flooding Grant Program, your out-of-pocket expense in 2026 will likely be just a fraction of the total plumbing bill. (For a comprehensive look at the entire program, read our complete London Ontario Basement Flooding Grant Guide).

Here is a transparent breakdown of what drainage contractors are charging in London, Ontario this year, and exactly how the municipal grant math works.

Average Contractor Costs in London (2026)

Installing a backwater valve is not a DIY project. It requires breaking the concrete floor of your basement, cutting into your main sanitary sewer line, installing the valve to the exact specifications of the Ontario Building Code, and patching the concrete.

Depending on the depth of your sewer pipe, the accessibility of your basement, and the contractor you choose, the total cost for a licensed plumber to install a backwater valve in London typically ranges from $1,500 to $3,000+.

Without financial assistance, this is a hefty bill. But that is where the City comes in.

How the 90% Municipal Grant Works

To encourage homeowners to protect their properties, the City of London offers to cover 90% of the eligible construction costs, up to a hard maximum of $1,800 for a backwater valve.

Here is how that math actually plays out on your invoice:

• Scenario A: The Affordable Quote
  Your plumber charges: $1,600
  The City calculates 90%: $1,440
  Your total out-of-pocket cost: $160
• Scenario B: The Standard Quote
  Your plumber charges: $2,000
  The City calculates 90%: $1,800 (This hits the exact maximum cap)
  Your total out-of-pocket cost: $200
• Scenario C: The Expensive/Complex Quote
  Your plumber charges: $3,000
  The City calculates 90%: $2,700 (This is over the cap, so the City drops the payout down to the $1,800 maximum limit)
  Your total out-of-pocket cost: $1,200

Beware the Quote Format Trap

While getting the city to hand you $1,800 sounds great, there is a massive catch. The City of London is incredibly strict about how your contractor’s quote is formatted.

If your plumber hands you an invoice that simply says "Supply and install backwater valve - $2,000," the City’s Sewer Engineering Division will reject your application. By-law A.-7562-160 dictates that all quotes must be explicitly itemized, separating the cost of materials from the cost of labor.

The Final Verdict: Is it Worth It?

When you factor in the City of London grant, paying $200 to $400 out of pocket to completely prevent raw municipal sewage from destroying your basement flooring, drywall, and family heirlooms is an absolute no-brainer.

Sewer Check Valve & Grant FAQs

We receive a lot of specific questions from homeowners regarding these devices. Here are the most common answers based on the City of London's program rules.