Drinking water that comes to your home, office or school through a tap is from either a public water supply or private well. Because people drink and use water every day, contaminants in drinking water have the potential to affect many people and be a major public health issue.
Information and Resources
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- What is a public water supply?
"Public water system" or “system” or "PWS" means a system that provides water to the public for human consumption through pipes or other constructed conveyances, if the system has at least 15 service connections or regularly serves an average of at least 25 individuals daily at least 60 days out of the year. A public water system is either a "community water system" or a "non-community water system." "Community water system" or "CWS" is a public water system which serves at least 15 service connections used by year-round residents or regularly serves at least 25 year-round residents. Any public water system serving 7 or more homes, 10 or more mobile homes, 10 or more apartment units, or 10 or more condominium units is considered a community water system unless information is available to indicate that 25 year-round residents are not being served.
Below is a table displaying the number of people in Wisconsin on a community water system.
- What is a private well?
A private well is owned by a person and is connected to their home and property. There are many regulations in place when digging and constructing new wells, however, once a well is in place there are few requirements for ongoing systematic monitoring. For more information please visit the Wisconsin Department of Natural Resources (http://dnr.wi.gov/topic/Wells/types.html).
The Wisconsin Environmental Public Health Tracking (EPHT) Program partnered with the University of Wisconsin at Stevens Point's Center for Watershed Science to develop a publicly-accessible mapping tool that provides private well data for multiple analytes at county, township, and section levels. (http://www.uwsp.edu/cnr-ap/watershed/pages/wellwaterviewer.aspx).
- What is the relationship between drinking water and health?
Because people drink and use water every day, contaminants in drinking water have the potential to affect many people. The number of people served by a community water system varies from less than twenty-five to over a million. Community water systems in the U.S. provide among the highest quality drinking water in the world. However, some contaminants are present at low levels, and it is still possible that drinking water can become contaminated at higher levels.
Since contamination in a single community water system can expose so many people at once, drinking water quality is an important public health issue.
- What are the health effects from exposure to drinking water
If a person is exposed to a high enough level of a contaminant, they may become ill. Effects can be short-term (where people become sick immediately) and/or long-term (where people get sick after a long period of time). There are many types of health problems that can result from exposure to contaminants. The type and severity of the health problem depends on the specific contaminant, the level of the contaminant in the water and the person’s individual susceptibility.
- How can I be exposed to contaminants in drinking water?
People can be exposed to contaminants in drinking water not only by drinking the water, but also by eating foods prepared with the water, breathing water droplets or chemicals released from the water while showering, or by absorbing chemicals through their skin while bathing.
- How do contaminants get into drinking water?
Drinking water can be contaminated by natural sources, like bedrock, or from man-made sources, like disinfection chemicals, agricultural run-off, or plumbing fixtures. Contamination can happen if there are new sources of contamination of the wells, reservoirs, lakes, or rivers that the water system uses, or if there are problems with the water treatment system.
- How is drinking water quality protected in Wisconsin?
For more information about drinking water quality and protection in Wisconsin please visit the Department of Natural Resources drinking water quality program.
- What are the primary sources of drinking water in the state?
Approximately, two-thirds of the states population drinks water from public supplies. Public water supplies provide water that has been obtained from either a surface or ground water source. For more information about drinking water sources in Wisconsin please visit the Department of Natural Resources drinking water quality program (http://dnr.wi.gov/topic/DrinkingWater/currentIssues.html).
One-third of the state’s population gets drinking water from private supplies. For more information about private wells and testing please visit the Department of Natural Resources (http://dnr.wi.gov/topic/Wells/privateWellTest.html).
- Why does drinking water source-surface or ground water-change
my public health risks?
The number and types of chemicals found in the source water depend on if the water comes from a surface water source or a groundwater source. The source water is the water that is used by each community water system to generate the clean drinking water. For more information about drinking water sources and water quality in Wisconsin please visit the Department of Natural Resources drinking water quality program.
- How do I prevent exposure to drinking water contaminants in my home?
To learn about preventing exposure to drinking water contaminants, visit the Bureau of Environmental and Occupational Health about Drinking Water.
- How does WI EPHT measure drinking water quality?
The data provided on this website can be used to help environmental health practitioners and the public to begin to understand and prioritize drinking water contamination issues. Data for the following contaminants are included on our website:
- * Nitrate
- * Arsenic
- * Disinfection by-products (2 types):
- - Total trihalomethanes (TTHM): Regulated TTHMs include Chloroform, Bromoform, Bromodichloromethane, and Dibromochloromethane.
- - Haloacetic Acids (HAA5): Regulated Haloacetic acids are: Monochloroacetic acid, Dichloroacetic acid, Trichloroacetic acid, Monobromoacetic acid, and Dibromoacetic acid.
- The concentration categories are as follows:
Contaminant Concentration Categories Nitrate <3, 3-<5, 5-<10, 10+ mg/L Arsenic <5, 5-<10, 10-<20, 20-<30, 30+ mcg/L TTHM <20, 20-<40, 40-<60, 60-<80, 80-<100, 100+ mcg/L HAA5 <15, 15-<30, 30-<45, 45-<60, 60-<75, 75+ mcg/L
For all contaminants, there are three measures. For mean concentration there is an annual measure and a quarterly measure. For maximum concentration there is an annual measure.
For each measure there are two indicators: the number of community water systems within specified concentration categories and the number of people served by systems within specified concentration categories.
- What is the public water use index?
The public water use index estimates the total population served by community water supplies within a county. The index is relative because the accuracy of population estimates provided by community water supplies varies and changes over time. Also, in Milwaukee county, the Milwaukee water system extends well beyond county boundaries, therefore, this measure provides only an index showing the relative population estimate of people served by community water supplies located within communities compared to the 2007 Census estimates of total county population. 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 vice versa for Milwaukee.
- What can the public water use index tell me about public
health risks and drinking water quality in my community?
Knowing the total population served by a community water supply (e.g., public water use index) can help track who would be at risk of an exposure to any chemicals found in community water supplies.
These population estimates can serves as the basis for deriving additional population specific indicators for estimating the proportion of an areas population that might be exposed to drinking water that has the potential to be harmful to human health. These indicators are based on estimates of the population found in the state Safe Drinking Water Information Databases and are strictly estimates, they are not the actual numbers. Also, these numbers can not be broken down by specific at risk populations to address any age related vulnerabilities. This is significant because often the low levels of contaminants in drinking water may be safe for the general population but would put more vulnerable populations such as the very young or very old at risk of getting sick.
- How can tracking drinking water improve public health?
The development of methods for describing the distribution of types of drinking water sources and systems across the state will help public health practitioners identify areas of greatest concern that might require more targeted policies, education and or areas for future study.
- Where can I go for more specific information about a
particular drinking water quality issue?
For more information about drinking water quality or specific contaminants of concern
please visit the following:
Wisconsin Department of Natural Resources
* http://dnr.wi.gov/topic/drinkingwater/ (Note: These data are updated frequently. For the most recent and up to date data and to find out more about drinking water contaminants in your own area please visit the DNR’s website or talk to your drinking water system provider for more information.)
Environmental Protection Agency
- For more information about drinking water quality or specific contaminants of concern please visit the following:
All external hyperlinks are provided for your information and for the benefit of the general public. The Department of Health Services does not testify to, sponsor, or endorse the accuracy of the information provided on externally linked pages.
Last Revised: August 21, 2014
The public drinking water data can be viewed by the contaminants shown below. Access the public drinking water contaminant data in the WI EPHT online database. Review the Data Details below to learn about interpreting the data.
- Arsenic in Public Drinking Water Data Query
- Haloacetic Acid in Public Drinking Water Data Query
- Nitrates in Public Drinking Water Data Query
- Trihalomethane in Public Drinking Water Data Query
What is the data source?
How does WI EPHT measure public drinking water?
The WI EPHT website provides public drinking water by each contaminant (Nitrate, Arsenic, Trihalomethane, Haloacetic acid) by measurements of:
- Annual number of community water systems by maximum concentrations by geography
- Annual number of community water systems by mean concentrations by geography
- Quarterly number of community water systems by mean concentrations by geography
- Annual number of persons by maximum concentrations by geography
- Annual number of persons by mean concentrations by geography
- Quarterly number of persons by mean concentrations by geography
What are some considerations for interpreting the data?
Below is a limitation to consider when interpreting public drinking water quality 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 those for Milwaukee will be high.
There are many factors to consider when interpreting the data for personal use:
- 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 ground water 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 number of population served.