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 preparing food 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. Household bleach is usually 5.25 to 8.25% chlorine. Don't use bleach that contain perfumes, dyes, or other additives. Be sure to read the label. Filter cloudy water before adding bleach. Using a clean container, add 1 teaspoon to each 5 gallons of water, or 1/4 teaspoon to a gallon of water. Allow the mixture to stand for 60 minutes before using.

Purifying tablets or chemicals designed for camping or backpacking can also treat water effectively. Always follow the directions on the package.

Note: Boiling, bleach and other treatments intended to destroy pathogens in water will not remove other pollutants such as chemicals or toxic metals. Also note that bleach will not kill some disease-causing organisms such as cryptosporidium. Boiling is the surest method to kill disease-causing germs.

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. 

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.