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Public Health - Seattle & King County

Cleaning a basement after a flood

Basements flooded with surface water, seepage through walls, or backflow from sewer lines often suffer little or no structural damage from the water, because the water inside braces the walls against the pressure of outside water and waterlogged soil.

How and when to pump water out

Use the following instructions for draining the water:

  • Do not drain water inside the basement until most of the water on the outside of the walls has gone down. This will prevent the walls from being pushed in or the floors from heaving.
  • If you have a large amount of water in your basement or if there is no basement drain, you may need to buy or rent a sump pump to get rid of the water.
  • If your electrical panel is located in an area of your home that has been flooded, you will be unable to use an electric sump pump unless you use a pump driven a 12-volt auto battery. A gasoline engine pump may be used if exhaust can be vented to the outside.
  • Start pumping water out of your basement if the water inside is higher than the flood water level outside. You may need a measure to determine this.
  • Stop pumping when the two water levels become equal.
  • Pump the basement water out at the same rate at which the flood waters recede.
How to clean the basement
  • Shovel mud from the basement as soon as all water has drained or has been pumped out to allow floors and walls to dry.
  • Remove silt and dirt stains by rinsing concrete walls and masonry foundation walls with a high pressure hose.
  • If stains remain on the walls, scrub them with a stiff bristle brush and household detergent. Begin at the top and work down. Rinse often with clear water.
  • Start drying the basement as quickly as possible in order to minimize wood decay or growth of mold.
  • Open all doors and windows to allow the moisture to flow outside.
  • Buy or rent a fan or dehumidifier to speed up the drying process.
  • If you are sensitive to mold or mildew, wear a mask or respirator containing an appropriate filter.
How to avoid shock hazards
  • Be careful before using any electric appliance in a house that has been flooded.
  • Never turn on wet electric appliances because they may cause an electric shock, overheat, or start a fire.
How to get rid of odors
  • If ventilation does not remove odors:
    • Mop concrete floor and walls with a bleach solution (3/4 cups of household bleach to a gallon of water.)
    • Rinse and dry after 5 minutes.
    • Open windows when applying the bleach solution.
  • Place a lump of dry charcoal in an open tin/metal container to absorb odors.