What to do in the first 24 hours after a flood

The damage a flood causes is not finished when the water stops. It continues, quietly, invisibly, for the next 24 to 72 hours as moisture migrates deeper into walls, floors, and ceilings, as mould begins establishing in saturated materials, and as structural elements that could have been saved start to deteriorate beyond the point where drying in place is viable.

The actions taken in the first 24 hours after a flood determine whether the restoration programme is measured in weeks or months, and whether the total cost is manageable or catastrophic. This guide gives you the correct sequence, in the right order, with the reasoning behind each step.

Hour 0 to 1: Make the Property Safe

Before anything else is touched, the property must be confirmed safe to enter. This is not a formality, it is a life safety question.

Electricity first: If flood water has reached or may have reached any electrical installations, plug sockets, light switches, fixed appliances, the consumer unit, do not enter until the relevant circuits are isolated. Turn off all circuits serving affected areas at the consumer unit. If you cannot safely reach the consumer unit, call an emergency electrician before entering the property. Water in contact with live electrical installations is potentially fatal.

Structural safety: Water that has been present for hours can undermine ground-floor slabs, soften earth around foundations, and compromise loadbearing elements in ways that are not always visually obvious. If there is any visible cracking, settlement, or movement in walls or floors, do not enter until a structural assessment has been carried out.

Gas: If there is any smell of gas, do not enter, do not operate any switches or electrical devices, and call the National Gas Emergency Service immediately on 0800 111 999.

Category 3 water: If the flooding involved any sewage, from a backed-up drain, toilet overflow, or sewer surcharge, treat all contact water as Category 3 biohazard. Wear waterproof boots, nitrile gloves, and a mask before entering. Do not allow children into the affected space under any circumstances until professional decontamination has been completed.

Read also- how to protect belongings during a flood

Hour 1 to 2: Stop the Water and Document Everything

If the water source is still active, isolate it before anything else.

• Mains stopcock, under the kitchen sink, in a ground-floor cupboard, or where the supply pipe enters the building. Turn clockwise to close.
• Central heating circuit, isolate at the boiler and drain if the burst is in the heating system
• Contact your water company if you cannot locate or operate the internal stopcock, they can close the external stop tap

Once the source is stopped and the property is electrically safe, your next action before touching, moving, or cleaning anything is documentation.

Photograph and video every affected area with timestamps:

• The full extent of water spread on ceilings, walls, and floors
• Any visible waterline on walls, mark the height with a pencil line before it dries
• All damaged contents in situ before anything is moved
• Any specific damage to structural elements, fittings, or installations

This is your insurance claim evidence. Loss adjusters assess from the point of their visit, which may be several days later. Your timestamped photographs at the time of discovery are what protect the full value of your claim against any attempt to understate the original extent.

Do not dispose of any damaged items before your insurer has confirmed you may. Keep damaged contents even if they appear beyond salvage, they are claim evidence.

Hour 2 to 4: Remove Standing Water and Soft Materials

Water that remains standing continues saturating building materials at depth. Remove it as quickly as equipment allows.

• Submersible pump, for significant standing water volumes, the fastest available method. Direct discharge to an appropriate external drain point.
• Wet/dry vacuum, for residual volumes after pumping and for water on carpets and flooring
• Mops and absorbent materials, last resort for final residue; inadequate for significant volumes

Once standing water is removed, extract soft materials from the wet zone:

• Carpets and underlay, hold enormous moisture volumes and significantly extend the drying time of the floor substrate beneath them. Roll, label for insurance, and move to a dry space.
• Rugs, cushions, and upholstered items, retain moisture and raise ambient humidity continuously. Move out of the drying zone while retaining for insurance assessment.
• Cardboard boxes and paper-based materials stored at ground level, absorb water and provide ideal conditions for mould. Move immediately.

For GOV.UK guidance on what to do after a flood, check: GOV.UK, what to do after a flood

Hour 4 to 8: Notify Your Insurer and Instruct Professional Drying

Call your insurer on the same day of the event, not the following morning, not after the weekend. Most policies have a condition requiring prompt notification. Get a claim reference number.

Two critical points most homeowners do not know:

Your policy requires you to mitigate: A duty to mitigate clause exists in virtually every home insurance policy. It requires you to take reasonable steps to prevent further damage. Waiting for a loss adjuster appointment that may be 3 to 10 days away while avoidable secondary damage accumulates is not mitigation, it is delay that can give the insurer grounds to reduce the settlement. Begin professional drying immediately.

Industrial equipment is covered: Professional structural drying, including industrial dehumidifier hire, air movers, and associated monitoring, is a standard insured cost under most home insurance policies. It is not an optional extra. It is what the insurer expects to pay for. You do not need to wait for permission to start. Notify, instruct, document.

Disaster Care Capital responds 24/7 across London. Call us the moment the water has been removed and you have notified your insurer. We deploy industrial drying equipment the same day, begin moisture mapping from the first visit, and contact your insurer directly, providing the documentation they require from day one.

Hour 8 to 24: Deploy Industrial Drying Equipment

This is the most important step in limiting secondary damage, and the one where the difference between the right equipment and the wrong equipment is starkest.

The 24-hour mould establishment window is real. Mould begins germinating on surfaces where moisture content is elevated above threshold within 24 to 48 hours. Structural timber above 20% moisture content begins to deteriorate. Plasterboard saturated beyond 72 hours starts losing structural integrity and increasingly moves from drying-in-place to strip-out territory.

The correct equipment combination:

Industrial desiccant dehumidifiers: For most UK flood events, particularly in autumn, winter, and spring when ambient temperatures are below 15°C, desiccant dehumidifiers are the correct primary equipment. They maintain full extraction performance at any temperature. Refrigerant units lose effectiveness rapidly below 15°C and can ice up in cold spaces. An industrial desiccant unit extracting 30 to 60 litres per day creates the vapour pressure differential that draws moisture out of building materials at a practical rate.

High-velocity air movers. Directed across wet wall and floor surfaces, air movers displace the humid boundary layer adjacent to the material, accelerating surface evaporation by 30 to 50% compared to dehumidifiers alone. Position to direct air across surfaces, not at them, to maximise boundary layer displacement without concentrated heat damage.

Seal the space. Close all windows and external doors once equipment is running. Every open window forces the dehumidifier to process unlimited external air of unknown humidity rather than the defined air volume of the sealed room. This applies even in summer, warm summer air typically carries more absolute moisture than the air inside a drying property.

Daily moisture monitoring. Take calibrated pin metre readings at a defined grid of points across all affected surfaces every one to two days. Record every reading. The dry standard, the moisture content of unaffected equivalent materials in the same building, is the target, not a fixed number and not elapsed time.

What Happens If You Wait

The consequence of waiting 48 or 72 hours before deploying professional drying equipment is not simply that the drying takes longer. The scope of the damage expands.

• Moisture penetrates deeper into masonry, timber, and floor substrate during every hour of delay
• Mould establishes within 24 to 48 hours and is significantly harder to treat once colonies are active
• Plasterboard that could have been dried in place at 24 hours often requires strip-out at 72 hours
• Contaminated water that was Category 2 at hour one becomes Category 3 as bacterial growth accelerates

A flood that is professionally responded to within 24 hours is a significantly different, and significantly cheaper, restoration project than the same flood responded to at 72 hours. Speed is the most important single variable in flood restoration outcomes.

Call Disaster Care Capital immediately after any flood event across London. We are available 24 hours a day, seven days a week. We respond within two to three hours, deploy industrial equipment the same day, provide insurer-grade documentation from day one, and coordinate directly with your loss adjuster throughout the restoration programme.

For ABI guidance on home insurance claims and flood events, check: ABI, flooding and home insurance

Conclusion

The first 24 hours after a flood determine the outcome more than any other period. Safety first, electricity, structure, gas, and contamination. Stop the water source, document before touching anything, remove standing water and soft materials, notify your insurer immediately, and deploy industrial drying equipment the same day. The mould clock starts at the moment flooding stops. Professional response within 24 hours produces a fundamentally better outcome than response at 48 or 72 hours.

Frequently Asked Questions

What is the most important thing to do immediately after a flood?

Confirm electrical safety before entering, water in contact with live electrical installations is a life safety risk. Once the property is safe to enter, stop the water source, document the full extent of damage with timestamped photographs before touching anything, and call your insurer to report the event and get a claim reference number.

Should I try to dry a flooded house myself?

Domestic drying equipment, fans, standard dehumidifiers, open windows, is not adequate for significant flood events. Domestic dehumidifiers extract 10 to 20 litres per day; industrial units extract 30 to 100+ litres per day. The difference determines whether drying happens within the 24-hour window that prevents mould establishment or extends into the 72-hour window where secondary damage is already accumulating.