Water Testing Bacteria, Nitrates & Arsenic

You should test your well water every year for coliform bacteria. If you are pregnant or have infants under six months of age, you should also check for nitrate. Water should also be tested if you notice any change in taste, odor or appearance or after flooding.


Nitrates (NO3) are an essential source of nitrogen (N) for plants. When nitrogen fertilizers are used to enrich soils, nitrates may be carried by rain, irrigation and other surface waters through the soil into ground water. Human and animal wastes can also contribute to nitrate contamination of ground water. In Benton and Franklin Counties, agricultural practices have been linked to elevated levels of nitrates in drinking water. Although any well can become contaminated by nitrates, shallow, poorly constructed, or improperly located wells are more susceptible to contamination. Nitrate levels in drinking water can also be an indicator of overall water quality. Elevated nitrate levels may suggest the possible presence of other contaminants such as disease-causing organisms, pesticides, or other inorganic and organic compounds that could cause health problems.

Who is at risk from high nitrates in drinking water?

The Environmental Protection Agency (EPA) has set the Maximum Contaminant Level (MCL) of nitrate as nitrogen (NO3-N) at 10 mg/L (or 10 parts per million) for the safety of drinking water. Nitrate levels at or above this level have been known to cause a potentially fatal blood disorder in infants under six months of age called methemoglobinemia or “blue-baby” syndrome; in which there is a reduction in the oxygen-carrying capacity of blood. The symptoms of blue-baby syndrome can be subtle and often confused with other illnesses. An infant with mild to moderate blue-baby syndrome may have diarrhea, vomiting, and/or be lethargic. In more serious cases, infants will start to show obvious symptoms of cyanosis: the skin, lips or nailbeds may develop a slate-gray or bluish color and the infant could have trouble breathing. A sample of the infant’��s blood can easily confirm a diagnosis of blue-baby syndrome. It is difficult to determine the true incidence of blue-baby syndrome in Washington State because it is not a reportable disease.

Others at risk from excess nitrates in drinking water are:

  • Pregnant women
  • Individuals with reduced gastric acidity, and
  • Individuals with a hereditary lack of methemoglobin reductase.

Testing recommendations:

The only way to know if your drinking water is contaminated with nitrates is to have it tested. If you own a single family (domestic) well, it is recommended that you test your water every three years for nitrates; more often if you live in an area with a history (ie. Farming Communities) of high nitrate levels or if someone in your home is at risk from nitrate contamination.

What to do if you have high nitrates in your drinking water:

If your drinking water sample tested above the MCL for nitrates and you or someone else in your home is at risk of developing health problems due to high nitrates, it is recommended that you do not drink the water. Find a safe, alternative water supply until you decide on a more permanent solution.

There is no simple way to remove all nitrates from your water. Finding and correcting the source of nitrate contamination is the best course of action. Although it is common to think of boiling, softening or filtration as a means of purifying water, none of these methods reduce nitrate contamination. In fact, boiling water that contains high nitrates can actually increase the nitrate concentration. Reverse osmosis, ion exchange and distillation units could conceivably provide home treatment for removing nitrates from water, but those processes can be complicated, expensive, and generally require routine maintenance. Activated carbon and other simple filters do not remove nitrates to any significant degree. Home treatment units are generally not recommended, particularly as a permanent solution to assure nitrate-free water for infant use.

Your only long-term option may be to find a new source of water. This can be achieved by either drilling a new well or connecting to a public water supply system that has acceptable nitrate levels. When selecting a new well (or looking for sources of nitrate contamination around your existing well), be sure to consider ALL possible sources of contamination. Unlike other contaminants, nitrates are not diluted and filtered out as water travels through soil, so water wells:

  • must be separated from possible sources of nitrate contamination, including both leaching and surface drainage such as barnyard runoff.
  • should never be within 100 feet of a septic system, where an opportunity may exist for wastes to enter the well.
  • should have a sanitary seal specifically designed for the top of the well casing. This seal must be correctly positioned, with all openings properly sealed, to disallow the entrance of any potential contaminant into the well casing and ultimately into the water source.

In addition, inspect surrounding areas within a 100 foot radius of the well for sources of pollution such as garbage, animal pens, barns and especially agricultural areas where nitrogen fertilizers can contaminate ground water (this includes your home garden).

More Info: online listing
WISCONSIN online listing
(608) 266-0245
Wisconsin Department of Natural Resources
101 S. Webster Street, TS-6
P.O. Box 7291
Madison, WI 53707-7921

How do I remove nitrate from my drinking water?

Nitrate may be successfully removed from water using treatment processes such as ion exchange, distillation, and reverse osmosis. Contact your local health department for recommended procedures. Heating or boiling your water will not remove nitrate. Because some of the water will evaporate during the boiling process, the nitrate levels of water can actually increase slightly in concentration if the water is boiled. Mechanical filters or chemical disinfectants, such as chlorination, DO NOT remove nitrate from water. Remember to have your well water tested regularly, at least once a year, after installing a treatment system to make sure the problem is controlled.