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Backwater valves in Ontario: the Building Code, the permit, and the city subsidies

A backwater valve keeps sewage from backing up into a basement through the drains. Basement flooding records are among the checks a buyer's report reads, and a permit for a valve shows up in the City's permit records. This page sets out what the Province and the cities publish, with the source and date for each line.

Page reviewed 22 Oct 2026. Every line names its source below.

Before you list: backwater valves and the city subsidies

80%

Toronto's subsidy pays up to 80% of the invoiced cost of a backwater valve (expanded 1 May 2026).
$1,600

Toronto's maximum per device, within up to $6,650 per property.
$2,000

Hamilton's Protective Plumbing Program grant, with a contractor from the City's pre-qualified list.
2cities

Toronto and Hamilton both require a building permit to install a backwater valve.

The short version

Ontario's Building Code requires a backwater valve where a drain "may be subject to backflow" and the fixtures are below the street or the upstream sanitary manhole cover (Article 7.4.6.4).
Toronto and Hamilton both require a building permit to install a backwater valve.
Toronto's subsidy (expanded 1 May 2026) pays up to 80% of the invoiced cost of a backwater valve, to a maximum of $1,600 per device, within up to $6,650 per property.
Hamilton's Protective Plumbing Program gives a grant of up to $2,000 with a contractor from the City's pre-qualified list, and up to $500 for a valve installed by a contractor outside the list.
A permit and a final inspection on file are part of the record a buyer's side reads. OfferDue states what the cities publish and gives no advice on plumbing.

1 May 2026Toronto's subsidy expands: up to 80% of the cost, $1,600 a device.

In detail

What the Building Code says

The Province's 2024 Building Code Compendium, Division B, Part 7, Article 7.4.6.4 ("Protection from Backflow") reads: "Except as provided in Sentences (4) and (5), where a building drain or a branch may be subject to backflow, a backwater valve shall be installed on every fixture drain connected to it when the fixture is located below the level of the adjoining street, or a backwater valve shall be installed to protect fixtures which are below the upstream sanitary manhole cover when a residential building is served by a public sanitary sewer."

The city subsidies

Each city sets its own program, amounts and conditions. The table quotes the two whose pages we could read on 22 October 2026; the program page is the current version.

City	What the City's program page says
Toronto	Basement Flooding Protection Subsidy Program (modified 18 June 2026): "up to $6,650 in subsidies per property" for eligible work completed on or after 12 November 2025. Backwater valve: "up to 80 per cent of the invoiced cost, to a maximum of $1,600 per device (maximum two devices)". Sump pump: up to $2,250; battery backup: up to $300; severing and capping the weeping-tile connection: up to $400. Downspout disconnection is not subsidized, but the downspouts must be disconnected from the City's sewer (or exempted) to qualify.
Hamilton	Protective Plumbing Program (modified 3 September 2026): "a grant (subsidy) of up to $2000 for the installation of a backwater valve and other eligible works", including downspout disconnection and a sump pump installed with a backwater valve. "Property owners who choose a contractor outside of the list will only be eligible for a maximum of $500 for the installation of a backwater valve." A loan of up to $2,000 is also offered.
Ottawa	The City runs a Residential Protective Plumbing Program; its page lists the current amounts and conditions.
Other Ontario	The municipality's water or building department says whether it offers a program.

The permit and the inspection

Toronto. The subsidy page lists: "Obtain a building permit to install a backwater valve", and "Request an inspection once installation is complete. Do not enclose or cover the valve before the inspection is complete." The contractor and any sub-contractors "must have a valid business licence from the City of Toronto, at the time of installation or service." Toronto's permit guide describes a "Standalone drain permit for installation of a backwater valve in a house with one or two dwelling units."
Hamilton. "Backwater valve installations require building permit", and "The Building Inspector inspects the contractors work." For the maximum grant, owners "will be required to select a contractor from the list of the City's pre-qualified contractors."

The records a buyer's side reads

Basement flooding and sewer records, the flood plain overlay and the permits on file for the address are public records, and a buyer's report reads them. The entries below name each record and where it is published.

Who answers questions

The City's building department answers questions about the permit, and the City's program page about the subsidy. A licensed plumber or drain contractor does the work. Who does what in an Ontario offer names each role and its public register.

Sources

Government of Ontario, 2024 Building Code Compendium, Part 7 Plumbing, Article 7.4.6.4 (updated 20 October 2026), checked 22 Oct 2026.
City of Toronto, Basement Flooding Protection Subsidy Program (modified 18 June 2026), checked 22 Oct 2026.
City of Toronto, Building permit application guide: backwater valve (modified 14 July 2026), checked 22 Oct 2026.
City of Hamilton, Protective Plumbing Program (modified 3 September 2026), checked 22 Oct 2026.
City of Ottawa, Residential Protective Plumbing Program, checked 22 Oct 2026.

A rule or a form can change after the date a line was checked; the source's own page is the current version. Spotted something out of date? Write to [email protected] and it goes on the corrections list.

Public-record information, not legal, financial, insurance or inspection advice. OfferDue reports what each record and official page shows, with its source and date. Back to for owners and sellers.