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Water Testing
Why should I test my Well water?
If you have a well, you should have it regularly tested to make sure your water is safe to drink. Well water can be susceptible to contaminants that can affect your health. Even if your well has been free of contaminants in the past, 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.
For new wells or building permits, you may be required to test your water to get it approved as a drinking water supply.
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 for information on pricing and the correct way to collect and send in a water sample. Snohomish County Health Department no longer provides water testing services.
More Resources
You can also find more information about water testing by visiting the following resources:
- PrivateWellClass.org's Help Center
- Department of Ecology's Information for Owners of Private Wells
Still have questions? Get technical assistance! Email SHD-EHQ@snoco.org
Water testing for existing wells
Regular water testing is recommended for all existing household water systems. For private wells, the contaminants below are recommended for routine testing because they are difficult or impossible to detect based on smell, taste, or appearance and can have rapid or severe health effects. They are also more common to wells.
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 alert you to fecal pollution that may be contaminating your well. Fecal pollution can come from various sources, such as a failing septic system or livestock manure nearby. Fecal coliform bacteria can cause illness in humans. Learn more about coliform bacteria from the Washington State Department of Health.
Nitrates
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.
Arsenic
Because the amount of arsenic in well water can vary throughout the year, test for arsenic once in the late summer and once again in the early spring to see if there are seasonal differences. You may also want to test if:
- You live in an area known to have naturally occurring arsenic in the groundwater (arsenic is naturally occurring in the Snohomish County region due to geological factors)
- You know of neighbors who have high arsenic in their wells
Long term exposure to even small amounts of arsenic can increase the risk of developing certain health conditions such as cancer, while consuming high levels of arsenic can cause immediate and severe health effects as well. Learn more about the health effects of arsenic from the Washington State Department of Health.
A note about arsenic: When wells are accepted as a source of drinking water 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 being accepted as a drinking water supply, and an arsenic disclosure form must be recorded onto the property title. 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. Washington State Department of Health has additional information on contaminants, including:
- Chromium
- Copper
- Cryptosporidium
- Disinfection byproducts
- Lead
- Manganese
- Per- and polyfluoroalkyl substances (PFAs)
They also have a helpful guide on what could be the cause if you notice something off with your well water.
You've tested your water, but what do the results mean?
The results of your test will show how much of each contaminant the lab tested for was present in the sample you provided. This shows a snapshot of your well water at the time the sample was taken. Snohomish County Health Department has established primary drinking water requirements to help determine if your water supply is safe to drink. You can use the table below to see if your well water falls within safe limits for certain contaminants. These are also the contaminants that must be tested for new wells or those seeking a building permit.
Maximum Contaminant Levels (MCLs): The MCL is the highest level of a contaminant allowed in drinking water and is set as close to the Maximum Contaminant Level Goals (MCLGs) as possible. MCLGs are the levels at which there are no known or anticipated health risks. Snohomish County Health Department requires wells in our county to be at or below the MCLs listed below before they can be accepted as a source of drinking water.
Secondary Maximum Contaminant Levels (SMCLs): These levels set standards for contaminants that may make your water have an unpleasant taste, odor, or appearance. These contaminants are not considered to have a risk to human health at the secondary maximum contaminant level. You may want to test for these contaminants if you have reason to believe something is off with your well water. For more information on SMCLs, visit the Environmental Protection Agency's page for Secondary Drinking Water Standards.
Contaminant | Level Type | Level Amount |
| Arsenic | MCL | 0.010 mg/L |
| Bacteria, coliform | MCL | 0 present* |
| Barium | MCL | 2.0 mg/L |
| Cadmium | MCL | 0.005 mg/L |
| Chromium | MCL | 0.1 mg/L |
| Fluoride | MCL SMCL | 4.0 mg/L 2.0 mg/L |
| Lead | EPA Action Level | 0.015 mg/L** |
| Mercury | MCL | 0.002 mg/L |
| Nitrate | MCL | 10.0 mg/L |
| Selenium | MCL | 0.05 mg/L |
| Silver | MCL | 0.05 mg/L |
| Sodium | No standard established** |
*Zero present using presence/absence method. | **In absence of an MCL established by the State Board of Health & EPA for lead and sodium, Snohomish County Health Department applies the EPA Action Level of 0.015 mg/L for lead. For sodium, it must be tested and an advisory will be sent if levels exceed 20mg/L.
For more information on the contaminants above, visit the Environmental Protection Agency's recommended water quality criteria page. This will also tell you the MCLs for other contaminants.
My water is contaminated, what do i do?
If your well water tests below safe limits, great! Keep up with regular testing and maintain your well properly to make sure your water remains safe. But what should you do if your water tests high for a contaminant?
if you have an existing well & are doing routine sampling
If you are conducting routine sampling for your existing well and it tests high for a contaminant above Health Department standards, contact the Health Department by calling 425-339-5250 or emailing SHD-EHQ@snoco.org. You can also follow the recommendations below:
Remove or fix any possible sources of contamination. Are there fertilizers being used or stored nearby? Are there sources of human or animal waste that could be reaching your well? Is there damage to your well head? Look around for possible contamination sources and correct the issue. For instance, if your well tests high for nitrates and you've been applying fertilizer on your yard near your well, stop applying the fertilizer and then retest to see if the nitrate levels are lower.
Bacteriological contamination and disinfection. If your water sample shows bacteriological contamination (unsatisfactory levels of coliform bacteria, fecal coliform or E. coli) follow the Health Department steps to disinfect your well.
if you are applying for any of the following
- New Individual Well
- Two-connection well
- Building permit served by an individual well
And your well shows high levels of a contaminant above Health Department standards, your well will initially be denied as a drinking water supply. Contact the Health Department staff conducting your review for options to move forward. Your well water may be subject to further testing or treatment until it can show results within safe limits.