Every year the EPA and Wisconsin Department of Natural Resources establish regulations that limit the amount of contaminants allowed in drinking water. These reports explain where your water comes from, the quality of your water and what it means for you.



Water Quality Report Quick Guide

How to read and understand water quality report data.

Sources of Water


Groundwater is any water that lies beneath the land’s surface, taking up space between soil, sand particles or the fractures of rock. When it rains, some of the water is channeled into lakes and streams or evaporates—but most seeps underground. This is groundwater.

The quality of groundwater is impacted by the types of rocks and layers in the earth where it is stored. When a well is drilled into the ground, the water fills the pipe and is brought to the surface with a pump.


Surface Water

Surface water is any water found above the surface of land like lakes, rivers and ponds. Surface water is easily contaminated because it is exposed to air, animals and human activity and is not filtered by rock and soil like groundwater is. Surface water usually does not contain as much mineral as groundwater.



Contaminant Types


Microbial contamination is the presence of bacteria, viruses or other live organisms in your water supply. Not all bacteria or viruses make people sick; some are simply a nuisance, generating taste or odor concerns.


Inorganic contaminants are compounds such salts, metals, lead or arsenic that can be in the groundwater naturally or introduced by runoff, industrial discharge, mining or farming practices.

Organic Contaminants

This group of carbon-containing contaminants includes pesticides and herbicides along with fuel byproducts and solvents. These contaminants are NOT naturally occurring and usually enter the water supply through runoff or by absorbing into the soil and eventually making their way downward to groundwater. These chemicals have been traced to landfills, industrial facilities and septic systems.


The Environmental Protection Agency regulates this type of contamination to protect public health. Erosion of natural deposits and discharges from nuclear power plants can contribute to radioactivity in groundwater.


Useful Acronyms 

Maximum Contaminant Level Goal (MCLG)

The level of contamination in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety.

Maximum Contaminant Level (MCL)

The highest level of contamination allowed in drinking water. MCLs are set as close to the maximum contaminant level goals as possible.

Action Level (AL)

The concentration of a contaminant which, if exceeded, triggers treatment or other requirements within a public water system.

Maximum Residual Disinfectant Level (MRDL)

The highest level of a disinfectant allowed in drinking water. Evidence suggests that the addition of a disinfectant is necessary to control microbial contaminants.

Maximum Residual Disinfectant Level Goal (MRDLG)

The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contaminants. 

Treatment Technique (TT)

A required process intended to reduce the level of contamination in drinking water.


Data Table Measurement Acronyms

  • ND = No detection
  • mrem/year = millirems per year (a measure of radiation absorbed by the body)
  • pCi/l = picocuries per liter (a measure of radioactivity)
  • ppm = parts per million, or milligrams per liter (mg/l)
  • ppb = parts per billion, or micrograms per liter (ug/l)
  • ppt = parts per trillion, or nanograms per liter
  • ppq = parts per quadrillion, or picograms per liter