Nearly 900,000 households rely on private wells as their primary water supply. Homeowners with
private wells are encouraged to have their well tested on a regular basis to determine the safety of the
water supply for purposes such as drinking and cooking. While testing is the only way to determine
the types and amount of contaminants in a well water system, homeowners and local officials often
want to know more about water quality issues in their community.
The WI Well Water Quality Interactive Viewer was created as an educational tool to help people better
understand Wisconsin's groundwater resources that many of us rely on for our drinking water.
How does the viewer work?
The viewer relies mostly on voluntarily submitted well water samples from homeowners and other well
water data collected by state agencies over the past 25 years. It would not have been made possible without
the many well owners who took the initiative to have their wells tested.
Because groundwater quality can often be very site specific for certain contaminants, many water
samples are required to get a sense of groundwater quality at a county or watershed scale. By combining
all of this data together we are able to look at averages or the number of samples that exceed drinking
water standards to get a sense of private well water quality across the state.
- Select a county, township or section to view water quality summaries at different scales.
- Select from one of 14 different water quality parameters.
- Areas that are blank show areas where insufficient well water data exists to summarize well
water quality for that area. But you can use the groundwater quality summary statistics tool to see
the number of samples that exist in a particular county, township, section or user defined area.
- Map colors can be adjusted for those that have trouble viewing certain colors or if you are printing
maps on a non-color printer.
The viewer does not show any problems where I live. Should I still have my water tested?
Yes, absolutely. The viewer is not a replacement for testing your well. Well water quality
is often very site or system specific. Every well should be tested for certain things depending on where
you live and the types of land-use activities in the area around your well.
Certain tests like bacteria are recommended to be tested for on an annual basis or anytime water changes
color, taste or odor. Water quality can also change so testing for things like nitrate on a regular basis
is important for tracking changes in water quality over time.
For more information on important tests to perform on a private well please download the brochure:
Tests for Drinking Water from Private Wells
Always have your water tested at a certified laboratory:
Laboratories certified to test for bacteria
Search laboratories certified for other contaminants
I am purchasing a new home, can the viewer locate water quality results for a particular well or property?
No. Anytime you invest in a new home or property with a private well we strongly encourage you to have it
inspected by a certified well inspector and have it sampled for some basic water quality concerns at that time.
Many of the results displayed in the viewer are voluntarily submitted well water samples and we cannot verify
the results of any one individual test result. Individual test results have the potential to misrepresent water
quality, both good and bad. For example, some homeowners submit samples that have passed through water treatment
devices that may make water quality appear better than it actual is. A past positive bacteria test may no longer be
an issue if an old well cap was replaced. Lastly, water quality can change over time. Many of the samples displayed
in the viewer may be years or even decades old and not representative of the well water at the time of sale.
Sampling the well prior to purchasing the property is the only way to know for sure the current water quality.
The value of the water quality viewer is in the amount of data displayed. It does a good job of showing areas
where water quality has been degraded or is more likely to exceed certain drinking water standards. It relies on
the law of averages and requires large numbers of samples in order to characterize water quality for a county or
town. The smaller the number of samples the less representative the information will be of water quality in an
area. The viewer is not a replacement for a water test and should not be used for site specific planning purposes.
Is groundwater quality getting better or worse?
The viewer is good at identifying areas where water quality issues exist. It is not designed to look at trends
in water quality over time.
Answering whether water quality is getting better or worse requires baseline data as a starting point and regular
monitoring of wells into the future. This viewer is a good start for communities to view baseline data and
identify areas where more data is needed. It can also help communities focus future water quality testing
efforts in areas where problems exist.
If the viewer is successful in encouraging private well owners to perform routine well water testing then in the
future we will have a better chance of answering whether groundwater quality is getting better or worse.