Water leak at home: what to do right away

A water leak can ruin a floor, a ceiling or a finished basement within hours. The first few minutes matter more than anything else: here is what to do, in order, before the plumber gets there.

1. Shut off the water

For a leak under a sink, behind the toilet or at the dishwasher, first close that fixture’s small shut-off valve. If water is coming from a pipe, a wall or the ceiling, or you cannot tell where it comes from, close the main water valve of the house. It is usually where the water pipe comes through the foundation, often in the basement, near the meter and on the street side.

Find it today, clear away anything stacked in front of it and check that it turns: a seized valve will not help on the night of a flood. Show it to everyone who lives in the house.

2. Watch out for electricity

If water reaches outlets, baseboard heaters, appliances or the electrical panel, do not touch them and do not walk in the water. Turn the power off at the panel only if you can reach it safely, standing on a dry floor. Otherwise, call an electrician, and if there is immediate danger, dial 9-1-1.

3. Limit the damage

• Open a faucet on the lowest floor to drain the water still in the pipes.
• If the water heater is leaking, also cut its supply: the breaker for an electric unit, the gas valve for a gas unit.
• Mop up, take out rugs and boxes, raise the furniture and air the room. Dry it as fast as you can: after a day or two, mould sets in (see our guide on mould and humidity).
• A ceiling that sags or keeps staining can give way: do not stand under it, and set a bucket at a distance.

4. A leak in Montréal: the outside valve and 311

The basement valve only protects the inside. According to the City of Montréal (page updated May 15, 2026, in French), the owner is responsible for the water supply piping from inside the building to the valve between the building and the main under the street. That outside valve, the water service box also called the bonhomme d’eau, may only be operated by City staff: do not try to close it yourself.

The City asks you to call 311 right away if a puddle spreads quickly on your lot, water is coming into the basement or through the walls, or you hear a constant hiss in the pipes. A request is urgent when there is no running water at all or when water getting in is damaging the inside of the home. The owner, or someone representing them, must be there when the water is shut off and turned back on; delays and fees vary by borough. In Repentigny, the City (in French) asks residents to call its public works department during office hours, and 9-1-1 after hours, in case of a sewer backup or water damage. Elsewhere, ask your municipality who closes the curb valve.

5. Photos, insurer, then the repair

Photograph the leak and the damage before any repair, keep the damaged parts and every invoice, and tell your insurer the same day. Our guide to a water damage insurance claim covers what comes next, from the notice deadline to the claims adjuster.

The repair is plumbing work: in Quebec, the company must hold an RBQ licence that includes subcategory 15.5. Ask for the number on the first call and check the licence before the plumber arrives. Once the emergency is over, you can browse plumbers in Montréal, in Laval or in Longueuil, or describe the repair to get quotes from licensed companies.