Water Testing 

Why should I test my Well water?

If you have a well, you should have it regularly tested to make sure the people living in your home are drinking clean water. Well water can be susceptible to many contaminants that can be harmful to your health. Even if your well has been tested in the past with great results, it's important to remember that things can change over time or even during different times of the year, so it is best to keep up with regular testing. See the Routine Testing tab below to learn how often to test your water.

If you are having a new well drilled or seeking a building or other well-related permit, you will need to have your water tested for multiple contaminants. This is a requirement before the Health Department can approve a permit.

Where can i have my well water tested?

Well owners can use the searchable map maintained by the Department of Ecology to find a lab that offers testing for drinking water. Contact the lab that you wish to use from the Department of Ecology's map for information on pricing and the correct way to collect and send in a water sample. The Snohomish County Health Department no longer provides water testing services.

  1. Routine Testing
  2. Understanding Your Results
  3. Help with High Levels

Water testing for existing wells

To help make sure your drinking water is safe, regular water testing is recommended for all existing household water systems. Owners of private wells should test their drinking water based on the recommendations below:

Coliform Bacteria

Test for coliform bacteria at least once a year, or when...

  • A household member has an unexplained illness
  • You hear your neighbor's well is contaminated or they have a failing septic system
  • You notice a change in your water's appearance, taste, or smell
  • You replace or repair any part of your well system
  • Your well has been flooded

Testing your water for coliform bacteria can tell you whether or not there is fecal pollution contaminating your well, either from a human source such as a septic system or an animal source such as livestock manure. Fecal coliform bacteria can cause illness in humans. Learn more about coliform bacteria testing from the Washington State Department of Health.


Test for nitrates at least once a year, or when...

  • A household member is an infant under 12 months old
  • A household member is pregnant, nursing, or trying to get pregnant
  • You live in an area where fertilizers are, or have been, used near your well

Exposure to nitrates above the recommended level can cause illness and death in infants below the age of six months. Symptoms include shortness of breath and blue-baby syndrome. Nitrates can come from fertilizer runoff, leaking septic tanks/sewage, or erosion of natural deposits. Learn more about the effects of nitrates in drinking water from the Washington State Department of Health.


Test for arsenic twice a year, once in summer and once in winter, or if...

  • You live in an area known to have naturally occurring arsenic in the groundwater (this is Snohomish County, we are in an area that is high in naturally occurring arsenic!)
  • You know of neighbors who have high arsenic in their wells

Arsenic is naturally occurring in the Snohomish County region due to geological factors. Arsenic levels in groundwater and wells can vary over time, even from season to season. For example, a water sample taken in June might show different arsenic levels than a sample taken in December, and a sample taken in 2015 might show different levels than one taken just a year or two later. If you drink water containing arsenic in excess of the safe limits over many years, it can cause health problems. Learn more about the health effects of arsenic from the Washington State Department of Health.

A note about arsenic: When wells are permitted in Snohomish County, the water must be tested for arsenic among other contaminants. Well water that tests high must have an approved treatment system installed before the well can be approved, and an arsenic disclosure form will become part of the property's title record. However, because arsenic levels can vary, a well drilled years ago may not have had arsenic at the time, but it could now. This is another reason to test your well water regularly.

What about other contaminants?

If you have a concern about other contaminants, you can get your well water tested. The Washington State Department of Health has additional information on contaminants, and a helpful guide on what could be the cause if you notice something off with your well water.