Dealing with flood or water damage?
Mold after water damage
Checked against FEMA and other official sources ยท Last reviewed October 8, 2026
Mold can start to grow when spores land on something wet, so the most important step after a leak or flood is drying. EPA says to dry water-damaged areas and items within 24-48 hours to prevent mold growth. If mold has already started, clean it up and fix the water problem; in most cases you can handle a moldy area of less than about 10 square feet yourself. CDC says that if you see or smell mold, you should remove it, and it does not recommend mold testing. [1][2]
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Why mold follows water damage
EPA says molds are part of the natural environment. They reproduce by tiny spores that float through outdoor and indoor air. EPA explains that mold "may begin growing indoors when mold spores land on surfaces that are wet," and that none of the many types of mold "will grow without water or moisture."
That is why EPA calls moisture control "the key to mold control." You cannot get rid of every spore in a house; some will always be in the air and in house dust. The spores will not grow if moisture is not present. If you clean up mold but don't fix the water problem, EPA says the mold problem will most likely come back.
Mold also damages what it grows on. EPA notes that "the longer it grows, the more damage it can cause," so act quickly. [1]
The 24-48 hour drying window
EPA's guidance is that "if wet or damp materials or areas are dried 24-48 hours after a leak or spill happens, in most cases mold will not grow." CDC gives the same window after a flood: clean up and dry out your home fully and quickly, within 24-48 hours.
CDC's guide for homeowners and renters goes further. If your home flooded and you were not able to dry it (including furniture and other items) within 24-48 hours, "you should assume you have mold growth." Mold may be hidden under or behind carpet, cushions or walls.
To dry a home after a flood, CDC recommends: - Remove standing water and wet materials. A wet vacuum can pull water from floors, carpets and hard surfaces. - Open all doors and windows while you work, and leave as many open as is safe when you leave. - When electricity is safe to use, run fans and dehumidifiers. But do not use fans if mold has already started to grow, because fans may spread the mold.
If water came from sewage or other contaminated water, EPA says to call in a professional who has experience cleaning and fixing buildings damaged by contaminated water. For the bigger picture of returning home, see what to do after a flood. [1][2][3]
Can you clean it yourself? The 10 square foot rule
EPA says size is one factor in deciding who should do the cleanup. If the moldy area is less than about 10 square feet (roughly a 3 ft. by 3 ft. patch), "in most cases, you can handle the job yourself."
If there has been a lot of water damage, or mold covers more than 10 square feet, EPA points to its more detailed guide, Mold Remediation in Schools and Commercial Buildings, which it says applies to other building types too. If you hire a contractor, EPA says to make sure the contractor has experience cleaning up mold and to check references.
A few other cases call for caution: - If you suspect your heating and air conditioning system is contaminated, EPA says not to run it, because it could spread mold through the building. - CDC says people with allergies, weakened immune systems, or chronic lung diseases such as asthma or COPD should not take part in mold cleanup. Children should not take part in disaster cleanup work. - If you have health concerns, EPA says to consult a health professional before starting cleanup. [1][3][4]
How to remove mold from walls and other surfaces
EPA's basic method for hard surfaces is to "scrub mold off hard surfaces with detergent and water, and dry completely." CDC's after-disaster steps are similar: clean with water and a detergent, remove all mold you can see, and dry right away.
Protect yourself first. CDC recommends at least an N95 respirator, goggles that give complete eye protection, and protective gloves (non-latex, vinyl, nitrile or rubber). If you will spend a lot of time removing moldy belongings or tearing out moldy drywall, CDC recommends a half-face or full-face respirator. EPA adds that a respirator must fit properly to be effective. Don't touch mold or moldy items with bare hands.
Two common mistakes to avoid: - Painting or caulking over mold. EPA says not to paint or caulk moldy surfaces; clean and dry them first. Paint applied over mold is likely to peel. - Killing mold without removing it. EPA notes that dead mold may still cause allergic reactions in some people, "so it is not enough to simply kill the mold, it must also be removed." [1][3][4]
What to throw away
Porous materials are the hardest to save. EPA says absorbent or porous materials, such as ceiling tiles and carpet, may have to be thrown away if they become moldy, because mold can fill the empty spaces and crevices and be "difficult or impossible to remove completely."
After a flood, CDC's rule is simpler: throw away anything that was wet with flood water and can't be cleaned and dried completely within 24 to 48 hours. [1][3]
Mold, insurance and flood policies
CDC's advice is to contact your insurance company and take pictures of your home and belongings before you start cleanup. Whether mold damage is covered depends on your policy, so check with your insurer. For how home policies handle leaks versus floods, see homeowners insurance and water damage.
If the water came from a flood and you have a National Flood Insurance Program policy, read its mold exclusion. The standard dwelling policy does not cover "water, moisture, mildew, or mold damage that results primarily from any condition" that is substantially confined to the dwelling or that is within your control, including "failure to inspect and maintain the property after a flood recedes." For the claim process, see filing a flood insurance claim. [3][5]
Keep mold from coming back
EPA's target for indoor humidity: "If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity." CDC's advice is stricter: keep humidity as low as you can, "no higher than 50%," all day long. A small humidity meter from a hardware store can measure it, according to EPA.
EPA's other moisture tips: - Fix plumbing leaks and other water problems as soon as possible. - Use air conditioners or dehumidifiers when needed. - Vent clothes dryers and other moisture-producing appliances outside where possible, and run the bathroom fan or open a window when showering. - Make sure the ground slopes away from your foundation, and keep gutters clean and repaired. - If you see condensation on windows, walls or pipes, dry the surface and reduce the moisture source quickly.
In a bathroom or other place that is often damp, EPA says more ventilation and more frequent cleaning will usually keep recurring mold to a minimum. [1][2]
Questions people ask
Does bleach kill mold?
Bleach can kill mold on hard surfaces, but EPA and CDC differ on when to use it. EPA says using a biocide such as chlorine bleach "is not recommended as a routine practice during mold cleanup," though professional judgment may call for it in some cases. CDC says bleach or dish detergent can be used, and if you use bleach, mix no more than 1 cup of household laundry bleach in 1 gallon of water. CDC also says that with only a little mold and minor water damage you may not need bleach, and that bleach cannot work on mold covered by mud and dirt that hasn't been removed. Open windows or doors when using it, and never mix bleach with ammonia or any other cleanser. EPA warns that mixing chlorine bleach with cleaning solutions that contain ammonia can produce toxic fumes. [1][4][6]
Is black mold dangerous?
CDC describes Stachybotrys chartarum as a greenish-black mold that grows on high-cellulose materials such as fiberboard, gypsum board and paper when there is constant moisture. CDC says it and other molds "may cause health symptoms that are nonspecific," and that no test exists that proves a link between Stachybotrys and particular health symptoms. CDC's guidance is that all molds should be treated the same with respect to potential health risks and removal, and that if Stachybotrys or other molds are found in a building, they should be removed. [7]
What are the symptoms of mold exposure?
CDC says damp and moldy environments may cause a variety of health effects, or none at all. For some people, mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash. People with asthma or mold allergies may have severe reactions, and people with weakened immune systems or chronic lung disease may get lung infections from mold. EPA adds that mold can irritate the eyes, skin, nose, throat and lungs of both allergic and non-allergic people. If you have persistent symptoms, CDC says to see your doctor. [1][2][7]
Should I get my house tested for mold?
Usually not. CDC does not recommend mold testing, and it says it is not necessary to determine what type of mold you have; whatever the type, you need to clean it up and fix the moisture problem. EPA says that in most cases, if visible mold growth is present, sampling is unnecessary, and that no EPA or other federal limits have been set for mold. EPA notes that surface sampling may help confirm that an area has been adequately cleaned, and that sampling should be done by experienced professionals. If you suspect hidden mold, such as a musty smell with no visible source, EPA suggests considering an experienced professional. [1][2][3][7]
How do I know the cleanup is finished?
EPA says the water or moisture problem must be completely fixed, visible mold and moldy odors should be gone, and the area should show no new signs of water damage or mold when you check back shortly after cleanup. CDC adds that if you still see or smell mold, you have more work to do, and that if health problems such as asthma or allergy attacks get worse when you return home, you may still have some mold. [1][3]
Sources (7)
- A Brief Guide to Mold, Moisture and Your Home, US Environmental Protection Agency. Accessed October 8, 2026.
- Mold, Centers for Disease Control and Prevention. Accessed October 8, 2026.
- Homeowner's and Renter's Guide to Mold Cleanup After Disasters, Centers for Disease Control and Prevention. Accessed October 8, 2026.
- Mold Clean Up Guidelines and Recommendations, Centers for Disease Control and Prevention. Accessed October 8, 2026.
- 44 CFR Part 61, Appendix A(1): Standard Flood Insurance Policy, Dwelling Form, eCFR (Code of Federal Regulations). Accessed October 8, 2026.
- Mold Clean-Up After Disasters: When to Use Bleach, Centers for Disease Control and Prevention. Accessed October 8, 2026.
- Facts About Stachybotrys chartarum, Centers for Disease Control and Prevention. Accessed October 8, 2026.