About one-third of Wisconsin’s population drinks from private wells. For many, private drinking wells can be a safe and dependable source of water. But unlike public water systems, the job of monitoring private wells for contaminants is the responsibility of the well owner.
Nitrate and bacteria are the two most common contaminants found in Wisconsin wells. Unfortunately, nitrate and bacterial pollution from agricultural fertilizer and manure applications, and to a lesser extent failing septic systems, have contributed to widespread private well contamination.
According to the Groundwater Coordinating Council’s 2025 Report to the Legislature, 4.4% of private wells tested that year exceeded the health-based drinking water standard of 10 ppm, but exceedance rates were as high as 25% in the central, south-central and western areas of the state. In Southwest Wisconsin, initial testing done as part of a large study completed in 2022 found that 42% of wells in Grant, Iowa, and Lafayette Counties were contaminated with bacteria and/or nitrates.
It’s important to test your water for these contaminants regularly to protect you and your family from associated health risks. Studies have shown that exposure to high levels of nitrate can cause Blue Baby Syndrome in infants, a condition that impacts how blood carries oxygen through the body which leads to weakness, increased heart rate, fatigue, and dizziness. Exposure to nitrates may also increase the risk of certain birth defects, thyroid disease, and certain types of cancer. While exposure to most bacteria does not always affect our health, some bacteria can make us sick. Certain types of bacteria can cause flu-like illnesses that lead to symptoms such as diarrhea, nausea, vomiting, cramps, and fever.
Because nitrates are tasteless and odorless, and bacteria and other pathogens can show up in your well without noticeable changes in your water, contamination can go undetected. Public health officials recommend testing your well for nitrates and bacteria at least once a year, especially if you live in a heavily agricultural area.
If you are concerned that your well may be contaminated, here are some steps you should take to protect you and your family from the health risks associated with consumption of polluted drinking water.
1. Begin testing your private well regularly.
Only 10% of people are regularly checking their private well quality. The Wisconsin Department of Health Services (DHS) recommends testing annually for bacteria and nitrate, and every five years for arsenic and lead. See DHS’s list of other contaminants to consider testing.
In some cases, contaminated well water will show symptoms in odor, appearance, or taste. If your water doesn’t seem normal, it could be contaminated. The DNR’s list of water quality symptoms can help you pinpoint the possible contamination issue and determine the right test to get.
2. Find a lab that can test for your suspected contaminant.
Once you’ve identified the contaminants you would like to test for, you’ll need to sample your well water and have it tested by a certified lab. We recommend contacting your local health department for help finding a certified lab, interpreting your test results, or identifying other potential testing programs in your area.
The DNR has an online list of state laboratories, instructions on collecting a water sample, and resources on understanding test results as well.
Unfortunately, these tests aren’t free, and the cost ranges depending on what you choose to test for. You may be eligible for no-cost testing through the Wisconsin Well Testing Access Program (WellTAP).
Make sure to review the testing specifications carefully before you pay for a test. While the price tag may give you sticker shock, having clean, safe drinking water is essential for you and your family, not to mention that the cost of testing your well could help prevent greater medical costs down the road.
3. What to do if your well tests positive for a contaminant.
If your well tests positive for contaminants, the first thing you should do is reach out to your local health department or the state Department of Health Services (608-266-1120). to help you review and interpret the test results with you. They may ask you to have another sample tested to ensure the results are accurate.
The DHS lists recommended actions you should take in the short-term, like finding another source of drinking water, like bottled water, as well as long-term solutions like choosing and installing a water treatment device. Find more information from DHS here.
You’ll need to consult with health experts about the right course of action if you believe you or others in your home are experiencing symptoms of water contamination exposure. In some cases, health experts may recommend that you see a physician. Depending on the contaminant and concentration, medical attention may or may not be necessary. Individuals who are more vulnerable to water contaminants — including people who are or may become pregnant, young children, people with weakened immune systems, and older adults — should act immediately. It is also important to note that chronic exposure to water contaminants can impact everyone, not just those most vulnerable.
The DNR has a list of certified contractors for hire that can help you drill a new well or install certain treatment devices, but be sure to first consult with state experts about the specific treatment you’ll need. You may also be eligible for DNR’s Well Compensation Grant Program which provides eligible well owners with financial and technical assistance to conduct further testing and replace, reconstruct, or treat your private well to remove the contamination. Find out who can apply for this program here: Well Compensation Grant Program
4. Find where the contamination is coming from.
Private well contamination requires both a pollution source and a pathway for the contamination to get into the aquifer. For this reason, you could have one risk factor but not the other and be okay.
It’s important to be aware of potential pathways for contamination, including things like shallow aquifers (pollutants from the surface have less distance to travel), aquifers overlain by materials that water-carrying pollutants can move quickly through (like sand or fractured karst), or cracks in the well casing.
Sometimes the source of private well contamination can come from your own backyard through things like fertilizer use or a leaky septic system.
But in many other cases, the source can be from something bigger, such as a nearby manufacturing facility, golf course or farm. If you believe your contamination is coming from an external source your county land conservation department may be able to help. Find your county land conservation department contact number by using the state-wide member directory. County land conservation departments have local knowledge of potential contamination sources from adjacent properties. They may have already determined where the contamination is coming from.
If you want to see broader contamination trends in your area, you can use the interactive Well Water Data Viewer map from the University of Wisconsin-Stevens Point. This tool uses voluntarily submitted private well data from around the state to map contamination patterns. While it’s not a definitive representative of groundwater quality in your region, it can give you a better idea of what contaminants have been found near you.
Lastly, we recommend checking out the Water WELLness tool to help manage your private well water system. Created by UW-Madison Extension and the UW-Stevens Point Center for Watershed Science and Education, the WELLness tool serves as a comprehensive guide to help guide you through well testing, result interpretation and what you can do to protect and improve your well water quality.
5. Make a plan to keep your well safe from contamination.
This is a problem we’re working hard to solve at Clean Wisconsin! Totally eradicating contamination in Wisconsin’s groundwater will be a societal effort, but there are steps that you can take to protect your own well.
- Slope the ground around your well away from the wellhead to keep runoff—which may contain pollutants—from draining toward your wellhead.
- Avoid using or mixing pesticides, fertilizers, herbicides, and other harmful chemicals near your well.
- Avoid damaging the well casing and make sure your well cap is secure and in good condition. It shouldn’t have cracks, holes, or other damage. See Learn About Private Water Wells for a diagram of the parts of a well.
- If you have a septic system, be sure to have it pumped and inspected at least every three (3) years for leaks and other signs that the tank or drainfields may be failing.
- Get your well tested at least once per year – contamination can happen at any time, so a clean well sample this year doesn’t mean it can’t become contaminated in the future!
6. Finally, be an advocate for clean water!
Connect with a Farmer-led Watershed Group that’s active in your community. The state supports local groups of farmers who are working together to expand water quality protection practices in their areas. Learning more about and interacting with your local farmer-led group helps increase communication and understanding about water issues and the role of agriculture in reducing water quality impacts.
Talk to your lawmakers! Let your elected officials know that clean drinking water is a priority for you and urge your elected officials to always prioritize protecting and providing clean drinking water when making decisions that affect your community, like new developments, land use changes, and agricultural permitting. You can do this easily by signing up for Action Alerts from Clean Wisconsin to speak up for our water at key moments.
Attend local, county, or state meetings. Vote. Find your local county board officials and meeting calendars by using MyVote Wisconsin.
