Private Well Testing Guidelines

Nitrate and Bacteria

The Minnesota Department of Health (MDH) Well Management Program oversees public and private wells in Minnesota. The MDH’s “Owner's Guide to Wells” states that the homeowner is responsible for regularly testing their well water. This includes laboratory analysis for bacteria annually and nitrate-nitrogen (nitrate) testing every other year.

Nitrate can occur naturally in groundwater at levels typically in the range of 0 to 3 parts per million (ppm). Human activities such as sewage disposal, livestock production, and crop fertilization can elevate the level of nitrate in groundwater. The drinking water standard for nitrate is 10 ppm; above this level nitrate can have negative effects on human health, specifically infants under the age of six months. For additional information the MDH has nitrate in drinking water resources online. You may also contact the MDH at 800-383-9808.


Pesticides are substances used to prevent, destroy, repel, or mitigate pests. Pests can be insects, animals, and weeds as well as microorganisms such as fungi, molds, bacteria, and viruses. Herbicides, fungicides, insecticides, and rodenticides are all considered pesticides. Once released into the environment pesticides often degrade over time into similar but distinct compounds called break-down products or degradates. An example is cyanazine. Cyanazine is an herbicide that was mainly used on corn crops in Minnesota from the early 1970s through the 1990s. Cyanazine use stopped in 2002 when the registration of this pesticide was voluntarily cancelled. Cyanazine breaks down in the environment into different chemicals. Some of the breakdown products of cyanazine have been detected in Minnesota water.

Pesticide analysis in water samples can be costly and the use of specific pesticides can vary throughout the state making it difficult to know which pesticide to analyze. General pesticide kits may not detect pesticides used in your area and may not provide an accurate analysis of compounds that may be present in your well. Based on this, we recommend that you contact the MDA prior to sampling your well for pesticides.

The cumulative or compounding health risk associated with low levels of multiple pesticides in drinking water is not well understood at this time. In general, vulnerable populations such as infants, children, and pregnant/nursing women are at greatest risk. For more information regarding the cumulative risk of pesticides in your water and diet please visit the MDH website “Evaluating Your Pesticide Risk.”

MDA Private Well Testing Programs

The MDA also conducts nitrate and pesticide sampling in private wells throughout the state of Minnesota. We are currently sampling wells for nitrate in townships with vulnerable groundwater and that have significant row crop production for nitrate as part of the Township Testing Program (TTP). More than 70,000 private wells owners will be offered nitrate testing in over 300 townships.  Homeowners are offered a pesticide test through the Private Well Pesticide Sampling (PWPS) Project if nitrate is detected in their first township testing sample. We anticipate that approximately 7,000 wells will be sampled for pesticides as part of the PWPS Project. 

Testing Laboratories

The MDH recommends using an accredited laboratory to test your water. To identify a laboratory to have your well water tested, go to Minnesota Department of Health (MDH) Certified Environmental Laboratories. The customized search tab on this page allows you to search for a laboratory that accepts samples from private homeowners. The MDH certifies laboratories that provide testing data to government agencies and other organizations, usually for regulatory purposes. MDH certification assures the client that the laboratory uses approved analytical procedures, follows quality assurance/quality control protocols, has properly trained staff, and reports data accurately. Currently, only one commercial lab in the nation (Weck labs in California) is able to analyze for cyanazine break-down products. The MDA is working with commercial labs to try to develop a lower cost test.

Home Water Treatment

If your test results indicate that there are agricultural chemicals present in your well water, options can include home water treatment. When possible, it is best to remove sources of contamination or replace a contaminated water supply with a safer water supply rather than rely on a home water treatment unit. Also, the cost to test for pesticides in water may exceed the cost of a point-of-use home treatment system, such as reverse osmosis for drinking water.

No single treatment process can remove all substances in water. If you decide to install a home water treatment unit, the unit (or units) you choose should be certified and labeled to reduce or remove the substance you are concerned about. If there is more than one substance you want removed from your water, you may need to combine several treatment processes into one system. However, in sampling conducted by the MDA, water from 44 private drinking water wells was sampled before and after it passed through the homeowners reverse osmosis system. The results indicated reverse osmosis home treatment systems removed 99.7% of pesticides that were evaluated, including 100% of the cyanazine break-down products. The reverse osmosis systems also reduced nitrate concentration to levels below the drinking water standard (10 ppm).

Even well designed treatment systems can fail. You should continue to test your drinking water after you install a treatment unit. If considering a treatment system, make sure the treatment unit is Underwriter's Laboratory (UL), or Water Quality Association (WQA) to remove pesticides. All home water treatment units require regular maintenance to work properly. Regular maintenance can include changing filters, disinfecting the unit, or cleaning scale buildup. You should always follow the manufacturer’s recommendations for installing, cleaning, and maintaining a treatment unit. For additional information on home water treatment technologies and grant and loan programs to pay for treatment please visit the MDH’s website on “Home Water Treatment.”