Public water systems are tested regularly for a variety of contaminants, but if you have a private well, routine testing is up to you. The Minnesota Department of Health and Scott County recommend that those who receive drinking water from a private well should be testing their water annually.

Educational Resources


Arsenic occurs naturally in rocks and soil across Minnesota and can dissolve into groundwater. Drinking water that contains arsenic can increase your risk of cancer and other serious health effects. Unfortunately, there is no way to know the arsenic level in water before a well is drilled. Arsenic levels can vary between wells, even within a small area. You cannot taste, see, or smell arsenic in your water.

The maximum level of arsenic the U.S. Environmental Protection Agency (EPA) allows in community water systems is 10 micrograms per liter (µg/L* or part per billion (ppb)). However, consuming water with arsenic at levels lower than the EPA standard over many years can still increase your risk of cancer. As a result, the EPA has set a goal of 0 µg/L of arsenic in drinking water.

Consuming water with even low levels of arsenic over a long time is associated with diabetes and increased risk of cancers of the bladder, lungs, liver, and other organs. Ingesting arsenic can also contribute to cardiovascular and respiratory disease; reduced intelligence in children; and skin problems such as lesions, discoloration, and the development of corns. Health impacts of arsenic may take many years to develop.

As of August 2008, well contractors test each newly drilled well for arsenic and share the results with the well owner and the MDH. Scott County combined the data maintained by the MDH and from the County Test Kits and from this data set found that 13% of these wells exhibited arsenic levels above the drinking water standard. See Arsenic Sampling Results Map (PDF).

If arsenic is detected at any level, consider:

  • Installing a treatment unit or
  • Using a different drinking water source.

Drinking water with even low levels of arsenic over many years increases the risk of diseases such as cancer. MDH highly recommends you take action if arsenic levels are above 10 µg/L. Water treatment units that reduce arsenic:

  • Reverse osmosis            
  • Distillation
  • Oxidation filtration
  • Adsorptive media
  • Anion exchange

Contact the MDH (651-201-4700) to talk with a water treatment specialist who can help you select the best option for you and your household. Water with arsenic is safe to use for other things (unless the level is above 500 µg/L). Since your skin does not easily absorb arsenic, your water is safe for washing dishes and clothes, brushing teeth, showering, bathing, and watering plants (including vegetables).


Nitrate is a common contaminant found in groundwater and surface water across the state of Minnesota.  Mainly, the increase of nitrate contamination in water is attributed to the increased usage of nitrogen rich fertilizers and pesticides in agriculture. Drinking water with concentrations of nitrate above 10 mg/L can cause immediate health problems.   Nitrate in drinking water has been linked to blue-baby syndrome (methemoglobinemia), certain types of cancer, and negative reproductive outcomes.  Nitrate consumption from drinking water is most damaging to young children and pregnant women. 

In areas of Scott County, specific glacially deposited soils lie above the bedrock aquifers that provide drinking water to people from private wells.  These soils are able to chemically remove the nitrates through a process called denitrification.  However, the glacial soils do not blanket the entirety of Scott County, and even where these soils do exist, the possibility of passage ways through the different soil and rock layers exist through fractures and weathering.  Also, wells that are completed in these layers are more susceptible to contamination as they are typically shallow compared to other bedrock reaching wells. 

Coliform Bacteria

Total coliform (TC) bacteria are common in the environment (such as in soil) and the intestines of animals and are generally not harmful. Fecal coliform (FC) and Escherichia coli (E. coli) bacteria are found in greater quantities than total coliform in animal fecal matter. If FC or E. coli is detected along with TC in drinking water, there is strong evidence that sewage is present; therefore, a greater potential for pathogenic organisms exists.  If coliform bacteria are present, the water supply should be disinfected and retested. If disinfection does not solve the problem, further treatment options may be necessary. 


Children and adults who drink water with high levels of manganese for a long time may have problems with memory, attention, and motor skills. Infants (babies under one year old) may develop learning and behavior problems if they drink water with too much manganese in it. 

  • If you have an infant who drinks tap water or drinks formula made with tap water, a safe level of manganese in your water is 100 micrograms of manganese per liter of water (µg/L)* or less.
  • If you have an infant who never drinks tap water or formula made with tap water, a safe level of manganese in your water is 300 µg/L or less.
  • If everyone in your household is more than one year old, a safe level of manganese in your water is 300 µg/L or less.

 Drinking water with a level of manganese above the MDH guidance level can be harmful for your health, but taking a bath or a shower in it is not. Manganese in your water can stain your laundry, cause scaling on your plumbing, and make your water look, smell, or taste bad. Manganese can also create a brownish-black or black stain on your toilet, shower, bathtub, or sink.


Well water in Minnesota usually does not contain detectable levels of lead. However, the pipes and other components in the household plumbing may contain lead. If they do, lead may dissolve into the water. The longer the water stands idle in the plumbing pipes and components, the more lead can dissolve into the water.

If any parts of your plumbing system were built before 1986, let the water run for at least 30-60 seconds before using it for drinking or cooking if the water has not been turned on in over six hours. This will "flush" the water that is standing in the plumbing pipes and components. You should do this for all faucets used for drinking and cooking. Flushing will remove much of the lead that may have dissolved into the water overnight. After an extended absence, such as a vacation, flush the system for twice as long as you normally do.