Water damage and mold: why the first 48 hours matter

Updated October 26, 2026. General information only, not professional advice.

After a leak, burst pipe or flood, the water you can see is only part of the problem. Water soaks into drywall, insulation, carpet pad and wood, and wet materials can grow mold. The EPA puts it simply: the key to mold control is moisture control. This guide explains what to do, in order, to give your home the best chance of drying out before mold takes hold.

The 24 to 48 hour window

The EPA says it is important to dry water-damaged areas and items within 24 to 48 hours to prevent mold growth. That is the one number to remember. It does not mean mold appears at exactly hour 49, and it does not mean everything is safe at hour 47. It means fast drying is the best protection you have, and the sooner you start, the better.

First hour: stop the water and stay safe

Stop the source. Shut off the main water valve for a plumbing leak. For outside flooding, wait until the water stops rising and officials say it is safe to return.
Keep away from electricity. Do not walk into water that may be touching outlets, cords, appliances or the electrical panel. Shut off power to the area only if you can reach the panel from a dry spot.
Think about what is in the water. Water from sewage or outside flooding can be contaminated. The EPA advises bringing in a professional with experience cleaning buildings damaged by contaminated water.
Protect yourself. Wear rubber boots and waterproof gloves. The CDC recommends rubber boots and plastic gloves for flood cleanup.

First day: document, remove water, start drying

Document first. FloodSmart advises taking clear pictures and video of damaged items before cleaning, fixing or throwing them out, and keeping receipts for repairs. Whether the damage is covered depends on your policy and the cause. Only your insurer can say, so contact them early.

Then get the water out and air moving:

Mop, towel or wet vacuum standing water. Use equipment rated for water, plugged into a dry outlet.
Move furniture, rugs, boxes and belongings out of wet areas.
Run fans and dehumidifiers. Open windows if the outside air is drier than inside.
Pull up wet area rugs, and lift wet carpet so air can reach the pad and subfloor.
Open cabinets and closet doors in wet rooms.

Second day: decide what stays and what goes

By now you should know what is drying and what is not.

Hard surfaces such as tile, metal, glass and sealed counters can usually be cleaned. The EPA says to scrub mold off hard surfaces with detergent and water and dry them completely.
Porous materials are harder. The EPA notes that ceiling tiles, carpet and similar materials that become moldy may need to be thrown away, because mold can be impossible to remove from them fully.
After a flood, the CDC advises throwing away items that cannot be disinfected, such as wall coverings, cloth, rugs and drywall.
FloodSmart advises immediately throwing away anything that could be a health risk, such as spoiled food or moldy clothing, cushions and pillows, after you have documented it.

If drywall or insulation is still wet after a day or two, it may need to be cut out so the wall cavity can dry.

Signs that mold has started

Visible spots or fuzzy growth on walls, ceilings, wood or fabric.
A musty smell that does not go away.
Stains or discoloration that spread.

Mold can also grow where you cannot see it, such as behind drywall, under flooring or inside cabinets. If you smell mold but cannot find it, a professional can look for hidden moisture.

Cleaning small areas yourself

The EPA says that if the moldy area is less than about 10 square feet, you can usually handle the cleanup yourself. If you do:

Fix the water problem first, or the mold will come back.
Wear gloves, goggles without vent holes, and an N-95 respirator, as the EPA guide recommends.
Never mix chlorine bleach with cleaners that contain ammonia. The EPA warns this can produce toxic fumes.
Dry everything completely when you are done.
Do not run your heating or cooling system if you think it may be contaminated with mold.

If anyone in the home has health concerns, the EPA suggests talking with a health professional before starting cleanup.

Keep it from coming back

The EPA recommends keeping indoor humidity below 60 percent, ideally between 30 and 50 percent, fixing leaks quickly, keeping gutters clear, and making sure the ground slopes away from the foundation.

When to call a pro

Call a water damage or mold cleanup company if the moldy area is larger than about 10 square feet, the water damage is extensive, the water came from sewage or outside flooding, or you cannot get materials dry within 24 to 48 hours. The EPA advises choosing a contractor with experience in mold cleanup and checking references.

Before you hire anyone, verify their license where your state requires one and ask for proof of insurance. Get a written estimate that describes what will be removed, how the area will be dried, and how they will confirm the job is finished.