Not in a flood zone? What the map doesn't show

Updated September 28, 2026

What the new maps represent

In short: the official map is about watercourse flooding. It shows neither rain pooling on a lot nor sewer backup. The FloodVerity screening looks at rain on the surface; it does not cover sewer backup either.

Since March 1, 2026, a modernized regulatory framework has replaced Québec's transitional regime for managing flood zones, shores and littoral zones. It relies on both old-generation and new-generation maps.

According to the Government of Québec (the page is in French), the new-generation maps represent only three types of flooding: open-water flooding, when a watercourse overflows after snowmelt or heavy precipitation; ice-jam flooding; and flooding where a flood-protection structure is present.

Zones are coloured in four intensity classes, from very high to low, which combine how often flooding may occur and the expected water depth. Where no new-generation map exists yet, the older maps of the municipality or the MRC remain in force.

What the map does not show: rain and sewer backup

Rain that runs off and collects on a lot, away from any watercourse, fits none of these three types. Even outside a flood zone, rain water can collect in a low spot, at the bottom of a reverse-slope driveway or along the foundation during a storm. The Insurance Bureau of Canada makes the same point: even far from a lake or a river, a house can be damaged by surface water or groundwater.

Sewer backup is a separate case. The Government of Québec also states that flooding caused by sewer or stormwater backup is not represented on the new-generation maps. It describes backup as an overflow of the urban pipe network, often after intense precipitation.

Neither the official map nor the FloodVerity check covers sewer backup: the screening follows rain water on the surface, not in the sewers. For that risk, ask instead about the backwater valve, the plumbing and the seller's answers (see our guide to the seller's declaration).

Checking an address on the official map

The government's tool “Check whether a property is located in a flood zone or in a channel migration zone of a watercourse” takes an address or a lot number. It shows sectors covered by old-generation maps, held by the municipality or the MRC, and the flood zones of the new-generation maps. These are published gradually and replace the old maps as soon as they come out for a sector.

In some sectors, the map shows “Présence possible de zone inondable” (a flood zone may be present). The government states that these data give a general idea, without precise limits, and have no legal value. To learn more, it refers you to the municipality or the MRC.

Greater Montréal: where the maps stand in September 2026

The Communauté métropolitaine de Montréal (CMM) has been preparing the new maps for its territory since 2019; preliminary maps were made public in September 2024. A first batch of approved maps was due to take effect on August 1, 2026, notably along the Rivière des Prairies, the Rivière des Mille Îles, Lac Saint-Louis and the St. Lawrence River. Québec postponed that date without setting a new one; on July 30, 2026, the CMM asked it to reverse that decision.

As of September 15, 2026, these maps were still unpublished, according to La Presse. As La Presse noted on August 4, 2026, in an article about downpours, these maps concern flooding caused by watercourses overflowing.

For rain, the CMM produced a map of zones sensitive to urban runoff: it locates cuvettes, the low areas where water collects, and the flow paths. Begun after the rains of August 9, 2024, it was shared with every CMM municipality in December 2025. According to the CMM, each municipality decides whether to make it public; these maps are indicative only and have no legal effect.

On June 24, 2026, La Presse reported that most municipalities had not made them public and that only the City of Montréal made its cuvettes map available. The article also notes that in these low areas, during exceptional rain, sewers cannot keep up, which leads to backups or infiltration. The Montréal map, produced in 2021 from LiDAR surveys, locates low spots with no natural drainage; it leaves out the sewer network, assumed saturated.

Where a rain screening fits

The official map answers a regulatory question: is the address in the flood zone of a watercourse? A rain screening asks another: where does the water from a heavy downpour go once it falls on the lot and around it? The FloodVerity check screens the area around one address for this, on the surface only, without the sewers; the published sample shows what a result looks like.

Run it after checking the official map, before you make an offer or during the inspection period, so you have time to ask the seller and the inspector where water collects.

The screening does not replace the building inspection, the opinion of an expert such as an engineer, the official flood-zone map or the municipality's information. It predicts no damage.

Sources

Check a house's address for $39

The check drops a 100-year, one-hour storm on the ground around the address and shows where the rain water collects. Result by email, no account.

You confirm the address on the next page, before paying $39.

See a sample result

Elsewhere on this site

These guides give general information, not legal, engineering or insurance advice. The FloodVerity check is a rain screening for one address, not a hydraulic study; it covers neither river and lake flooding nor sewer backup.