Flood zones in Belgium: what to know before buying

The official maps

Wallonia

The flood hazard map is “the reference tool in Wallonia” according to the Public Service of Wallonia (SPW). It covers two situations:

• overflowing watercourses, shown as hazard zones;
• runoff in dry valleys, shown as hazard axes.

The hazard has four levels: very low, low, medium, high. It combines the frequency of the event and its scale (water depth or flow). The maps are based on scenarios with a return period of 25 years and more: a mapped zone can therefore be flood-prone without having been flooded recently. On 17 April 2025, the Walloon Government chose a “rolling” revision: the map will be updated as new data arrive.

It can be consulted on the Wallonia Geoportal (WalOnMap), with the LIDAXES layer for runoff. According to the SPW, the map can be updated every 6 years.

Brussels

The Bruxelles Environnement (the Brussels environment agency) map (2025 version) can be consulted by address. You click on a 10 m² square to find out the cause (rain, river, rising groundwater, sewer), the frequency and the potential water depth. If no square appears, no risk is modelled at that location.

The map is indicative: an unmapped location is not guaranteed to be free from flooding, and a mapped location is not certain to be flooded, because individual protections are not modelled. For sewers, the modelling is incomplete (73% of buildings).

What the seller must disclose

The notary’s model sale agreement provides, for each Region, a “flood zones” clause.

• Wallonia: the seller declares whether or not the property is in a zone of the Geoportal mapping with a low, medium or high risk, from overflowing or from runoff. They also declare whether they know the property has already been flooded and describe the extent. The buyer is informed that this situation may lead to restrictions or a refusal of a permit, at the administration’s discretion.
• Brussels: the seller declares whether the property is in a low, medium or high hazard zone, or outside any zone, with a reference to the Bruxelles Environnement mapping.

The SPW also writes that notaries must inform the buyer of a property’s situation in relation to the flood hazard at the time of the sale. This does not exempt you from looking at the map yourself before the compromis.

An unmapped zone is not a guarantee. The SPW points out that land that has already been flooded may be missing from the map, and that the commune’s Planning and Environment departments often know about it. It strongly recommends making enquiries there before any purchase. If the map does not match the land, you can provide the administration with evidence proving it. See also planning information.

The effect on planning permission

In Wallonia, the map is consulted for permit applications: the CoDT (the Walloon Territorial Development Code) requires the competent services to be consulted when the project is in a flood hazard zone. The commune can refuse the permit or attach conditions to it. For an official opinion on a preliminary project, the SPW cites planning certificate no. 2 (certificat d’urbanisme n°2), to be requested from the commune. If you are buying to build or to renovate extensively, read buying building land.

Insurance

The high hazard zones of the Walloon map correspond to the “risk zones” of the Act of 25 June 1992 on land insurance contracts. The SPW explains what this means:

• insurers can refuse to cover properties located in these zones;
• they can refuse to cover a building constructed in a risk zone, 18 months after the publication of the new zone;
• the high hazard meets two criteria of the Royal Decree of 12 October 2005: a recurrence of 25 years or less and a water depth of at least 30 cm.

Before signing the compromis, ask your insurer what they would cover for this precise address. Add to the compromis a condition precedent linked to insurance if the property is in a hazard zone. If you are borrowing, talk about it early with your credit broker.

What to do in practice

1. Type the address into the Region’s map (WalOnMap or the Bruxelles Environnement map).
2. Note the hazard levels: overflowing, runoff, sewer, groundwater.
3. Ask the seller whether the property has already been flooded.
4. Ask the commune what it knows about the neighbourhood.
5. Get a price for the insurance.
6. If you want to convert or extend, ask for a CU2 before buying.

Which professional to consult

The insurer or an insurance broker says what would be covered at this address. The notary includes the seller’s declaration in the compromis. An architect can assess the possible works or the protections to plan. For precise measurements on site, a surveyor (géomètre-expert) can help.