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Homeowner help
for private wells.
Property transfers
and inspections.
Drillers and installers
resources and information.
drinking and groundwater.
Little boy at kitchen sink.

Keep your family safe by testing your water at least once a year.

Contact information
For information on this page, contact:
Liesa Lehmann
Section chief
Private Water Supply

Test your private well water annually

Make sure you’re serving your family safe drinking water. While most private water wells in Wisconsin provide safe drinking water, some may become contaminated with bacteria and other pollutants that are not filtered out when the water soaks into the ground.

Recommended testing

DNR recommends you test your private well at least once a year for coliform bacteria contamination and any time you notice a change in how the water looks, tastes or smells. Even if your water looks, tastes and smells good, it can contain harmful bacteria and viruses.

Bacteriological Contamination of Drinking Water Wells [PDF]

You may want to test for other contaminants, like nitrate, arsenic or agricultural chemicals.

The U.S. Geological Survey can help you understand what water quality is like in your county and contaminants you may want to test your water for.

Protecting Groundwater in Wisconsin through Comprehensive Planning [exit DNR]

Get started testing your water

Contact a certified laboratory that can test your water for a specific contaminant.

  • Labs certified to test for coliform bacteria [PDF] - an indicator that disease-causing bacteria may be present in the water
  • Labs certified to test for other contaminants

Collect a water sample properly

Collecting a water sample for testing isn’t as easy as turning on the tap. In fact, well owners frequently get false positives because they do not properly collect the sample or get it to the laboratory within the 48 hours required for an accurate test.

The laboratory you work through will provide you with a water sampling kit. It’s very important to make sure you follow their sampling directions.

Watch a demonstration showing the DNR’s recommended methods for of how to properly collect a water sample that will yield accurate results.

When to take action immediately

Your test results and the next steps you take differ by contaminant.

Most important contaminants

  • If the lab reports the sample as bacteriologically unsafe or at risk, stop drinking your water. For more information, see
    Bacterial Contamination of Drinking Water Wells [PDF].
  • If the lab reports elevated levels of nitrates, avoid drinking the water if you’re pregnant and stop giving the water to infants younger than six months or using the water to prepare infant formula. For more information, see
    Nitrate in Drinking Water [PDF].
  • If the lab reports elevated levels of arsenic (greater than 10 parts per billion), you may want to stop drinking the water. For more information, see
    Arsenic in Drinking Water [PDF].

Other contaminants

If the lab reports elevated levels of other contaminants, follow the steps described in the brochures for that particular contaminant. For more information, see frequently asked questions about Water Quality and Contamination in Private Wells.

Last revised: Wednesday September 28 2016