Using a dehumidifier after a leak or flood

Safety first

If water has reached sockets, light fittings, the consumer unit or any electrical appliance, turn off the electricity at the consumer unit if it is safe to do so, and have an electrician check before you switch back on. Do not stand in water to operate switches. Water coming through a ceiling can bring the ceiling down, so keep out from under bulging plasterboard.

Turn off the water at the stopcock if the leak is from your supply, and fix or isolate the source before you start drying.

Note:Never use electrical equipment, including a dehumidifier, on a wet floor or near standing water. Get an electrician if water has reached any wiring or sockets.

Step 1: remove the water you can see

Mop, squeegee or use a wet and dry vacuum to remove standing water. Lift wet rugs and soft furnishings and take them somewhere they can dry or be assessed. Move furniture off wet carpet, and put foil or blocks under legs that must stay.

Take photos of everything before you move or throw anything away. Your home insurer will want them.

Step 2: set up the room for drying

Close the doors and windows of the wet room so the dehumidifier is working on that air, not the whole house. Keep the room warm; compressor dehumidifiers work much better at normal room temperatures than in a cold room. If the room is unheated, a desiccant model is often the better choice, because it keeps working in the cold.

Place the dehumidifier in the middle of the room with space around it. A fan pointed at wet walls and floors speeds evaporation. Set the unit to continuous or the lowest humidity target for now, and use a drain hose if it fills its tank quickly.

1. 1

   Close doors and windows to the wet room

2. 2

   Keep the room at a normal room temperature

3. 3

   Put the dehumidifier centrally on a dry floor

4. 4

   Set continuous or the lowest target

5. 5

   Point a fan at wet surfaces

6. 6

   Empty or drain the tank and check twice a day

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Step 3: track progress

The tank will fill fastest in the first days, then less as materials dry. That slowing is a good sign but not proof the walls are dry. A damp meter used in the same spots every day, compared with a dry wall elsewhere in the house, shows when readings have levelled off. Our guide on damp meter readings explains how to use one.

Plaster and brick dry from the surface inwards and can stay damp behind for weeks. Do not redecorate, re-lay flooring or fit new skirting until readings match the dry comparison, or trapped moisture can cause damage and mould later.

How long it takes

There is no single answer. A small leak onto a hard floor may dry in a few days. Soaked plaster, a wet solid floor or water trapped under flooring can take weeks. Thicker and denser materials take longer. Keep the room warm and closed, keep the dehumidifier running and keep checking readings.

When to call professionals and your insurer

For larger leaks and floods, call your home insurer early. Many policies cover escape of water and will arrange a drying company with industrial dehumidifiers and moisture mapping. Tell them about any drying you have already started. A drying company can also check for water trapped under floors and inside walls.

If mould appears during drying, clean small patches as described in how to remove black mould, and keep humidity low.

Frequently asked questions

How long should I run a dehumidifier after a leak? Until damp meter readings in the affected area match a dry wall elsewhere in the home. That can be days for a small leak and weeks for soaked walls.

Should I heat the room while drying? Yes. Normal room warmth helps a compressor dehumidifier work well and speeds evaporation. In cold rooms, a desiccant unit is better.

Can I paint once the wall looks dry? Wait until readings confirm it is dry inside, not just on the surface, or paint may blister and mould may grow.