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Water Quality

Drinking Water Contaminants

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 Dakota County recommend that well owners annually test drinking water from private wells.

The Minnesota Department of Health provides information on common drinking water problems.

The following contaminants are the most common in Dakota County:

Coliform bacteria
The presence of coliform bacteria are disease-causing microorganisms that may indicate fecal contamination.   The water supply should be disinfected and retested. If the bacteria persist after repeated disinfection treatments, contact the Water Resources Department for recommendations by calling 952-891-7000.

Nitrate is derived naturally from air, soil, rock and plants in low concentrations.  High concentrations in groundwater are often associated with human and animal wastes, fertilized and irrigated crops, and landfills.  High nitrate concentrations in your water supply may indicate the presence of other contaminants that have not yet been tested or detected.

A water supply with a concentration of nitrate of more than 10 milligrams per liter indicates a significant risk to infants six months of age and younger. Infants consuming water and water-prepared formula and food containing more than 10 milligrams per liter of nitrate may be prone to methemoglobinemia or "blue-baby" disease. 

Older children and adults can ordinarily tolerate higher levels of nitrate without acute disease symptoms.  Boiling water that is high in nitrate only increases its concentration and does not make the water safe to drink.

Manganese is naturally occurring in our aquifers, possibly from the weathering of shale. Manganese is an essential nutrient; however, excess manganese can be neurotoxic, affecting memory, attention and motor skills. The drinking water standard for manganese in private wells is 100 micrograms per liter (ug/L) for bottle-fed infants 12 months and younger, 300 ug/L for everyone older than 12 months.

Many wells in the County have been tested for manganese and many exceed the standard of 100 ug/L; the results range from 0 to 1,790 ug/L. There are several water treatment options that can reduce manganese in drinking water. MDHManganeseTreatmentTable.pdfSee the Minnesota Department of Health Manganese Treatment Table.

Arsenic is naturally occurring in the groundwater in Minnesota.  There are a variety of health concerns for long-term exposure to arsenic. See the Minnesota Department of Health’s website for more information.

About 10 percent of the wells in Minnesota exceed the drinking water standard of 10 milligrams per liter (mg/L). Very few wells have exceeded the standard in Dakota County, but very few wells have ever been sampled for arsenic in the County.  It is now required for all newly constructed wells to have a water sample analyzed for arsenic. 

The Minnesota Department of Health recommends that a well be sampled at least one time for arsenic. There are several water treatment options that can reduce arsenic in drinking water such as: reverse osmosis systems with pre-oxidation, distillation or special removal medias developed by water treatment companies to reduce arsenic.

A pesticide screen is a relatively low cost and highly sensitive technique to detect the presence of various groups of pesticides in water. It does not indicate which specific pesticide(s) within a group may be present. The test will confirm the presence of pesticides, within the groups tested, at concentrations above a specified limit. Get your water tested.

The immunoassay may indicate the presence of some of the pesticide breakdown products within a particular group. Dakota County offers a combination of the following two pesticide immunoassay screens:

  • Triazine screen: This test will indicate the presence of common triazine herbicides, including atrazine (AAtrex), cyanazine (Bladex), and simazine (Princep).
  • Lasso/Dual/Acetochlor screen: This test will indicate the presence of alachlor (Lasso), metolachlor (Dual), or acetochlor (Harness).

Herbicides most commonly found in Dakota County private wells include: alachlor, metolachlor, atrazine, cyanazine, and acetochlor or their breakdown products.

Last updated: 5/17/2016 6:46 AM