Environmental Public Health Tracking: Water Data

Drinking water that is piped into your home, school, or office comes from either the public water supply or a private well. 

Wisconsin Tracking provides data and information on public water quality in Wisconsin.

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The section below presents answers to frequently asked questions about drinking water and the data.

Where does our water come from?

About two-thirds of Wisconsinites drink water from public water supplies. In these cases, water comes from either a surface or a groundwater source. For more details you can visit the Department of Natural Resources (DNR) drinking water quality website. One-third of residents get their drinking water from private wells. For details on private wells and well testing, visit the DNR private well page.

What is a public water system?

A public water system gets water to a community through municipal pipes. Public water systems must have at least 15 connections or serve at least 25 people daily. Water systems meeting this definition year-round are known as “community water systems.” Wisconsin Tracking provides data about community water systems on our public data portal. More information can be found on the Wisconsin Department of Natural Resources webpage.

What is a private well?

Private water wells are those that are owned by individuals, rather than the state or a city, and are connected to their home and property.  The Wisconsin Department of Natural Resources has rules in place to make sure new wells are safe. Once a well is in place, there are fewer rules for upkeep.  As a result, not all private wells are regularly tested for things that can make us sick. 

Wisconsin Tracking is working to improve private well water testing and link people to data on this topic.  Wisconsin Tracking partnered with the Center for Watershed Science at the University of Wisconsin - Stevens Point to develop a mapping tool. This tool maps decades of private well data at county, township, and section levels. 

Who makes sure public water is safe?

The state government protects water quality in Wisconsin through a number of laws and regulations. Wisconsin Tracking and organizations such as the Wisconsin Department of Natural Resources (DNR) work to improve and protect Wisconsin’s water quality.  For more information about water quality in Wisconsin, please visit the DNR drinking water quality website.

I have a private well. How do I make sure my water is safe?

How can my water make me sick?

Drinking water can become unsafe by natural sources, such as bedrock, or from human-made sources, such as chemicals, fertilizers, or old plumbing. Water can become unsafe at the source (wells, reservoirs, lakes, or rivers), or problems might occur during water processing (like problems in a water treatment system).

People can come in contact with harmful chemicals and bacteria through drinking water in many ways. They can drink bad water, eat foods made with bad water, breathe in polluted water droplets while showering, or even absorb these harmful chemicals through their skin while bathing.

Coming in contact with a high level of a harmful chemicals or bacteria can make you sick.  The type of illness and how sick you become depends on what the chemical or bacterium is and how much you came in contact with. It can also depend on your age, genetics, and medical history. Some symptoms of coming in contact with unsafe water quality include diarrhea, vomiting, cramps, and eye/nose irritation.

What is the data source?

Wisconsin Tracking hosts data from the Public Drinking Water System, maintained by the Bureau of Drinking Water and Groundwater of the Wisconsin Department of Natural Resources.

How does Wisconsin Tracking measure drinking water quality?

Wisconsin Tracking has data that can be used to help health professionals and the public understand drinking water issues.  Data for the following chemicals are included on our public data portal:

  • Nitrate
  • Arsenic
  • Disinfectant by-products
    • Total trihalomethanes (Chloroform, Bromoform, Bromodichloromethane, and Dibromochloromethane)
    • Haloacetic Acids (Monochloroacetic acid, Dichloroacetic acid, Trichloroacetic acid, Monobromoacetic acid, and Dibromoacetic acid)
  • Atrazine
  • Di (2-ethylhexyl) phthalate (DEHP)
  • Radium
  • Tetrachloroethene (PCE)
  • Trichloroethene (TCE)
  • Uranium

For each chemical listed above, there are four measures:

  • Number of community water systems by maximum concentrations
  • Number of community water systems by mean concentrations
  • Number of people served by community water systems by maximum concentration
  • Number of people served by community water systems by mean concentrations

To learn more about these chemicals, visit the Environmental Contaminants in Drinking Water section of the Water Issues page.

What are some considerations for interpreting the data?

  • For counties surrounding Milwaukee County that receive water from the Milwaukee system, their estimates of total population served by community water supplies will be low and estimates for Milwaukee will be high.
  • The measures do not account for the variability in sampling patterns and number of repeated samples that may be taken from the same system.
  • Concentrations in drinking water cannot be directly converted to exposure because water consumption varies between individual people.
  • Data and information about contamination in drinking water from private wells or other unregulated sources of drinking water are not captured in these measures.
  • A groundwater distribution system may draw water from multiple wells, and each well may have different concentrations of the contaminant. Compliance samples are taken at each entry point to the distribution system. In systems with separate wells that serve some branches or sections of the distribution system, the value calculated for the system would tend to underestimate the contaminant concentration for people served by wells with higher concentrations, and overestimate concentration values for people served by wells with lower concentrations.
  • These numbers are estimates and are not the actual numbers of population served.

Where can I learn more about drinking water quality?

Last Revised: March 24, 2021