What to Do Immediately After a Flood (First 24 Hours)

The first day after a flood is dominated by one thing: hazards. Before any cleanup, documentation, or restoration can begin, the people involved have to be safe and the building has to be confirmed safe to occupy. This reference lays out the first 24 hours as an ordered sequence — safety, re-entry, utilities, documentation, and the beginning of drying — drawing on federal and standards-body guidance. It is informational and not a substitute for instructions from local emergency authorities.

For the broader picture of why floodwater is handled the way it is, see the flood cleanup and safety pillar. For why floodwater itself is treated as a biohazard, see is floodwater dangerous.

Step 1 — Wait until it is safe, then approach carefully

The single most important rule is not to rush back. Federal guidance is explicit that you should return home only after authorities indicate it is safe, and then approach with caution. Ready.gov Floodwater conceals risk: it can undermine foundations, float vehicles, hide downed power lines, and carry sewage and chemicals. Rapidly moving water of even modest depth can knock an adult off their feet, and roadways may be washed out beneath standing water.

When you do approach the building, look at it from the outside first. If the structure is visibly shifted, if there are cracks in the foundation or walls, if the roofline sags, or if the building has moved off its footing, treat it as unsafe and do not enter until a professional has evaluated it.

It also helps to understand why the wait matters. In the hours immediately after water recedes, the most dangerous conditions are often the least visible: a foundation that has been undermined, a floor that looks solid but is no longer fully supported, live electrical circuits in contact with water, and gas lines that may have shifted or sheared. Emergency authorities clearing an area to re-entry is not a formality — it reflects a judgment that the most acute, life-threatening hazards have passed. Returning before that point trades a small saving in time for a disproportionate risk. If you evacuated, also confirm that roads and bridges along your route are open and sound, since flood damage to infrastructure can persist long after the water in your home has dropped. Ready.gov

Step 2 — Control the obvious hazards before entering

Before stepping inside, run through the hazards that injure or kill people during the recovery phase rather than the flood itself.

Electrical

Do not enter a flooded building if water is in contact with outlets, the electrical panel, or appliances, and never touch electrical equipment while standing in or on wet ground. CDC If you can reach the main breaker without standing in water and without risk, shutting off power is the safer default. If you cannot reach it safely, leave it to a qualified electrician or the utility.

Gas and fuel

If you smell gas or hear a hissing or blowing sound, leave immediately, leave the door open, and contact the gas utility from a safe distance. Do not use matches, lighters, or anything that could create a spark, and do not switch electrical devices on or off. Ready.gov

Carbon monoxide

A large share of post-disaster deaths come from carbon monoxide produced by generators, pressure washers, and other fuel-burning equipment run indoors or near windows. Never operate a generator, grill, or gasoline engine inside a home, basement, garage, or near any opening. CDC Keep this equipment well away from the building.

Step 3 — Treat floodwater as contaminated

Once inside, work on the assumption that the water is dirty. Federal health guidance treats floodwater as potentially carrying sewage, chemicals, fuel, and sharp debris, and warns that contact can cause illness, infected wounds, and skin and gastrointestinal problems. CDC The IICRC S500 standard generally classifies intruding surface floodwater as Category 3 — grossly contaminated water.

In practice this means: wear waterproof boots and gloves, avoid skin contact, keep cuts covered, do not let children or pets into affected areas, and wash thoroughly after any contact. CDC The reasoning behind that classification — and the specific organisms and chemicals of concern — is covered in is floodwater dangerous.

Water and food safety

Do not assume tap water is safe. Listen for boil-water notices, and do not drink, brush teeth with, or prepare food using water that may be contaminated until authorities confirm it is safe. EPA Discard food, including canned goods with damaged seals, that has come into contact with floodwater. CDC

Step 4 — Document everything before you move it

Once the building is safe to occupy, documentation comes before cleanup. Photograph and record video of the damage as you found it — exterior, every affected room, standing water lines on walls, and damaged contents — and build a written inventory of losses. This evidence supports insurance claims and federal assistance applications, both of which generally expect proof of the condition before items are moved or discarded.

Contact your insurer as soon as practical to report the loss and ask what they require. Flood damage is generally not covered by a standard homeowners policy and is instead handled through separate flood insurance, most commonly the National Flood Insurance Program; the distinction matters for who you call. See water damage insurance basics for how coverage is typically structured.

Step 5 — Begin removing water and drying out

Mold is the reason speed matters once hazards are controlled. Under the right conditions, mold can begin growing on wet materials within roughly 24 to 48 hours, so the early hours are when drying decisions pay off most. EPA

The general sequence is:

• Remove standing water by safe means once power hazards are addressed.
• Increase ventilation and air movement — open windows and doors when weather allows, and run fans and dehumidifiers if it is safe to use electricity.
• Remove saturated porous materials. Carpet, cushion, drywall, and insulation soaked by Category 3 floodwater generally cannot be reliably sanitized and are typically removed rather than dried. IICRC S500
• Clean and disinfect hard, non-porous surfaces that can be salvaged.

For the standards that govern when materials are dried versus discarded, and the mold thresholds that follow a flood, see the mold remediation standards reference.

What can usually be saved

Not everything is a loss. As a general guide, hard and non-porous items tend to be salvageable while soft and porous items soaked by floodwater tend not to be. Sealed concrete, metal, glass, glazed ceramics, and solid hardwood furniture can typically be cleaned and disinfected. Clothing, bedding, and washable textiles can often be laundered in hot water, though heavily sewage-contaminated fabric may not be worth saving. Documents, photographs, and electronics are special cases: they are frequently damaged beyond ordinary cleaning, but freezing wet documents to stop deterioration, and having electronics professionally evaluated rather than powered on, can sometimes preserve them. The default question for any porous item is whether it can be thoroughly cleaned, disinfected, and dried before mold sets in; if not, it generally goes.

Special hazards that are easy to overlook

Several flood hazards cause harm precisely because they are not obvious in the moment.

Standing water and slips

Wet floors, especially when coated in silt, are extremely slippery, and stairs are particularly dangerous. Move deliberately and assume every wet surface is a fall risk.

Wildlife and pests

Floodwater displaces animals. Snakes, rodents, and insects may take shelter in flooded structures and debris piles, so use caution when reaching into dark or submerged spaces and when moving stored items. CDC

Mental and physical fatigue

Recovery work is exhausting and emotionally taxing, and fatigue leads to mistakes around exactly the electrical, structural, and chemical hazards that injure people. Pace the work, stay hydrated, take breaks, and do not attempt heavy or risky tasks alone.

The first 24 hours, in order

• Stay out until authorities say it is safe; approach cautiously and check the structure from outside. Ready.gov
• Control hazards — electrical, gas, and carbon monoxide — before and during entry. CDC
• Treat floodwater as contaminated; protect skin, water, and food. EPA
• Document the damage thoroughly before moving anything, and notify your insurer.
• Begin drying quickly — the mold window is roughly 24 to 48 hours. EPA

The first day is about preventing the flood from causing a second round of harm — injury, illness, fire, or mold. Cleanup and rebuilding follow once the hazards are under control. For the wider safety framework, see the flood cleanup and safety pillar.