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data about the quality of groundwater near homes or businesses or get an estimate of groundwater availability.
the quality and quantity of groundwater for your family, business customers and community.
where your groundwater comes from and how it moves underground to reach your drinking water well and the lakes and streams you enjoy.

GCC Report to the Legislature Public Awareness of Groundwater Health Risk

Unlike public water systems, protection and maintenance of a private well is largely the responsibility of homeowners. The agencies use a variety of ways to increase awareness and promote testing. Many recommendations for which contaminants private well owners should test for are location-specific, but some contaminants should be tested for by all private well owners.

The GCC agencies recommend all private well owners test their water at least once a year for coliform bacteria, so the percent of potable private wells tested annually for total coliform bacteria can be considered a proxy for groundwater health risk awareness.

Of the estimated more than 700,000 potable private wells in Wisconsin, about 31,000 total coliform samples were taken annually on average during the past 5 years (2013-2017)*. Therefore, the average percent of potable private wells tested annually for total coliform bacteria is about 6% statewide. This is similar to results from a recent public health survey** that found that about 10% of private well owners have tested their well for any contaminant in the past year. Total coliform is by far the most frequently analyzed contaminant; around 30% of all reported sample results for private wells are for total coliform.

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* Estimating the number of total coliform samples — the number of total coliform samples in each county is estimated from four data sources:
1. samples required by NR 812.41 after new construction or pump work in potable private wells;
2. samples voluntarily reported to the Lab Data Entry System (primarily from the Wisconsin State Laboratory of Hygiene);
3. samples voluntarily reported to the Groundwater Retrieval Network; and
4. samples analyzed by the UW–Stevens Point Water and Environmental Analysis Lab.

Samples are screened for overlap between the first three sources and there is no expected overlap with the fourth source. This does not account for any samples analyzed at a private or local lab that are not subsequently reported to one of these four sources, so this approach likely underestimates the total number of samples. Statewide, the magnitude of this underestimate seems balanced by the underestimate of the number of wells, but this may vary from county to county.

**Schultz, A., Malecki, K. C. 2015. Reducing Human Health Risks from Groundwater: Estimating Private Well Testing Behaviors and Water Use among Private Well Owners in Wisconsin.

Last revised: Thursday August 30 2018