Flood Sanitation

Floods, earthquakes, and other disasters in Snohomish County can damage or contaminate your well, so it is important to be aware of health and safety precautions. For tips and resources, please review our Cleaning Up After a Flood Guide (PDF).

Flooded wells, safe water alternatives

If your well is not tightly capped or properly sealed, sediment and flood water can enter and contaminate your well. Wells most likely to be contaminated, even if damage is not apparent, include:

  • Drilled wells
  • Dug wells
  • Wells less than 50 feet deep


Flood waters might be contaminated and can make you sick if you drink it or eat flood-contaminated food.

Do not use water from a private water system that’s been flooded. Use only boiled or treated water. Bring the water to a full rolling boil for 1 minute before using. Water for brushing teeth, washing dishes or foods, requires the same treatment as drinking water.

If you need large quantities of water, or if boiling is inconvenient, use ordinary liquid household chlorine bleach to treat the water. Add 1/2 teaspoon to each 5 gallons of water, or 8 to 10 drops to a gallon of water. Double the amount of bleach for cloudy or colored water. Allow the mixture to stand for 30 minutes before using.

Disinfecting & Testing Your Flooded Well

After the flood water has receded, follow the CDC’s steps for disinfecting your well.

Test your well water after the well disinfection and before you begin drinking it again. The Snohomish County Health Department provides water sampling bottles for you to test your water. There is a fee payable when you drop off the water sample. Pick up and turn in your bottles for testing at the Snohomish County Health Department:
Environmental Health Division
Water and Wastewater Program
3020 Rucker Avenue
Suite 104
Everett, WA 98201-3900

Flooded septic system

If the water table is high or your sewage system is threatened by flooding, there is a risk that sewage will back up into your home. To prevent this back-up, you must relieve pressure on the system by using it less. Do not try to pump or use the system until water in the drainfield area is lower than the water level around your home.

Once flood waters have receded, you may need to address issues with your septic system. To properly care for your septic system after a flood, follow these tips from the Environmental Protection Agency or see our list of certified septic contractors in Snohomish County.