How to Prevent Mold After Water Damage

Flood Water Damage

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Water damage in a home is bad, but the resulting mold can be even worse. Once you dry out your home from the water damage—burst pipes, leaky water heater, groundwater intrusion, or a flood that affects your area—mold can grow for long afterward.

Understanding how mold develops, where to locate water damage, and what to do about it will help you prevent mold after water damage.

Why Mold Develops After Water Damage

No single factor creates mold. A combination of water, food, temperature, and time create the conditions that allow mold to grow after water damage.

  • Water: Water, either in liquid or airborne form, is necessary to create mold. Humidity levels of 80-percent or more especially will trigger mold growth.
  • Food: What is sometimes termed "food" for mold growth is some type of organic product such as the wood content in drywall paper, glues, or simply dust, dirt, and other loose debris.
  • Temperature: Temperatures of 80°F or higher are usually necessary to grow mold.
  • Time: Mold does not occur immediately after the water damage. Under certain conditions, it will take a few weeks for the mold to develop.
  • Oxygen: Oxygen is required to grow mold. Yet to prevent mold growth, much ventilation will be required to dry out the area.

Where to Locate Hidden Water Damage

Water damage is often evident when you see standing water, watermarks on a wall, or blistered paint. Other times, water creates damage you may not know about because it is more hidden.

  • Behind wallpaper
  • Back of drywall
  • Inside walls
  • Under carpet
  • Under carpet padding
  • On insulation
  • Between siding, housewrap, and house sheathing
  • Framing studs
  • Wall floor plates
  • Door trim


Because water can also move by capillary action, pay attention to any area where the water may wick. Absorbent materials like fiberglass insulation can carry the water higher than the original flooding height.

Tips for Mold Prevention After Water Damage

Work Quickly

Timing is important for preventing mold growth after water damage. The faster you work, the less chance of mold growth.

Studies show that, under optimum conditions for mold growth, mold will develop around 5 weeks after the flooding. Most mold remediation experts recommend drying out the area far earlier than that.

Remove Water

For large water events, start with the wet/dry shop vacuum that you may already own. As soon as possible, rent an industrial-grade wet/dry vacuum from your local rental yard or home center. These models have large tanks, up to 55 gallons. Some models have pump discharges.

Use Fans to Dry the Area

To avoid losing time, begin with any available fans you may have on hand. Box fans push air at a rate of only 1,820 CFM (cubic feet per minute). Rentable 36-inch industrial fans are capable of moving over five times as much air.

Use Dehumidifiers for Continued Drying

Rent industrial-quality dehumidifiers to dry out the air faster. Even inexpensive rental dehumidifiers can pull 18 to 20 gallons of water from the air per day, plus they have automatic pump-out features that help you avoid constantly emptying the water tank. Fairly robust consumer-grade dehumidifiers can only absorb around 5 gallons of water per day and have small tanks (under 1 gallon).

Start With the Worst Contaminants

Differentiate between clear water, gray water, and black water damage. Clear water is visibly clean, though still will contain microbes. Gray water is dirtier and comes from sinks, showers, and washing machines. Black water, the dirtiest, is contaminated with human or animal waste. If possible, clean up the black water damage first before proceeding to the gray and clear water damage.


Dispose of as much unwanted waterlogged material as possible. Disposal is the only way to ensure that the material will not develop mold weeks later. Remaining materials that have even a trace amount of moisture can possibly grow mold.

Stay Aware

Once done, keep aware of red flags that may mean that the water hasn't been eliminated or that mold is growing. A musty smell in the area likely means that mold is developing. Check areas by touch or with a moisture meter to see if they are completely dry. Two-by-fours, carpeting, or drywall may look dry but will feel wet when you touch or test them.


Biocides are substances used to kill microorganisms such as those that contribute to mold. As long as no mold has developed and the area is properly maintained, there is no need for biocides. Biocides on clean materials do not prevent mold growth.

How to Prevent Mold After Water Damage

  1. Secure House

    Turn off the power to the flooded area. Turn off natural gas or propane devices in the area on the devices and at the gas meter. Open windows to air out the house. If you smell gas after airing out the home, notify the gas company.

  2. Turn on Fans

    Turn on all available fans to blow from the outside to the inside of the house. Use these fans until you are able to rent high-velocity, long-throw fans.

  3. Turn on Dehumidifiers

    Turn on the dehumidifiers and keep them running constantly.

  4. Clean or Dispose of Black Water Damage

    Wear gloves, eye protection, and an N-95 mask when disposing of or cleaning black water-damaged items. Dispose of any unwanted items damaged by black water such as toys, pillows, and bedding.  Wash other contaminated items in the washing machine with detergent and hot water.

  5. Clean Gray and Clear Water Damage

    Remove pooled and standing water by bailing it out with a bucket (if deep enough) or by vacuuming it up with a wet/dry vacuum. If there is no electricity to the immediate area, run extension cords from the nearest power source. If using a generator, do not run it in or near the house or garage. Hard items damaged with clear, clean water can be dried out and then cleaned with soap and water.

  6. Pull Up Carpeting

    Wet carpeting must be pulled back well beyond the wet section, padding included. In cases of severe flooding, you may need to pull up all of the carpeting. Water that has reached underneath the padding will not dry out on its own. Direct fans toward the carpet, padding, and subfloor.

  7. Remove Drywall

    Waterlogged drywall cannot be reused. Pull out wet drywall, working upwards. For partially wet walls, stop 6 to 12 inches above the wet sections. If the water damage is less than 48 inches high and the drywall sheets were hung horizontally, the seam provides a convenient stop point.

  8. Dry Wood Framing

    Wood studs can usually be saved after water damage as long as they are gradually dried out. Do not try to quickly dry them out with heaters or heat guns. Rent or purchase a moisture meter to accurately determine if the wood is completely drying before adding drywall.

Tips for Preventing Mold Before Water Damage

Eliminate the conditions that encourage mold growth or which make it more difficult to properly clean up the water damage.

  • Clean carpeting: Dirt in and under carpeting contributes to mold just as much as water. Regularly vacuum the carpeting and occasionally have the carpet professionally cleaned.
  • Install mold-resistant drywall: After you've torn out the water-logged drywall, replace it with mold-resistant drywall that has a treated core and a fiberglass mat facing, not paper.
  • Install a wall vapor barrier: After removing the old insulation and drywall, use a polyethylene vapor barrier for the new insulation.
  • Install mold-resistant foam insulation: Sprayed foam and foam board insulation products are mold-resistant. Foam boards work well for framing against concrete or block basement walls.
  • Keep fiberglass clean: Fiberglass insulation is actually a poor material for encouraging mold growth since it's made of spun glass fibers and plastic. Dirt, debris, and water do encourage mold growth, though. So, if you decide to use fiberglass insulation, keep it clean and dry.
  • Use dehumidifiers: Use consumer-grade dehumidifiers on a regular basis to keep the humidity level down to 50-percent or lower.
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Final Report of The Hydrolab Project 2001 Flooring, Humidity, and Mold Growth. Carpet and Rug Institute

  3. Should I use bleach to clean up mold? EPA

  4. You Can Control Mold. CDC