Contaminants can enter the environment through natural sources as well as human activities. When contaminants enter groundwater they can influence the quality and safety of drinking water and impact human health.

Some contaminants in well water, like bacteria and nitrates, can cause short-term illnesses (such as stomach problems, diarrhea, nausea). This may be especially dangerous for certain high-risk populations such as small children, pregnant women, elderly, or people with a compromised immune system.

Drinking water with high levels of contamination for many years may increase the risk of long-term (chronic) diseases such as anemia, high blood pressure, and in some cases, cancer.


The risk from drinking contaminated water depends on the length of time you are drinking the water and how much of the contaminant you ingest. The health effects of exposure to any substance also depend upon:

  • How you are exposed (such as through breathing, drinking, or skin contact)
  • Your individual risk to a contaminant
  • Whether other chemicals are present

How are contaminants classified?

The US Environmental Protection Agency (US EPA) has identified around 80 contaminants that can impact drinking water quality. Of these, the contaminants are divided into two classes: primary and secondary contaminants.

Harmful contaminants have been detected in private well water in North Carolina. View maps and tables showing concentrations of contaminants found in private wells in each county of the state.

Primary contaminants

Primary contaminants can cause changes to your health if you are exposed to them in levels that are above the regulatory standards for a long period of time.

Secondary contaminants

Secondary contaminants can bother homeowners because they can change the taste and smell of the water, or cause staining of household fixtures. Secondary contaminants are not likely to hurt health and are not banned in public drinking water supplies.

Maximum Contaminant Levels (MCL)

The US EPA regulates contaminants in public drinking water supplies and sets standards for drinking water quality. The MCL is a legally enforceable standard for the highest level of a contaminant that is allowed in drinking water. The MCL is established to protect human health from contaminants in drinking water while also considering the best available treatment technology and costs. The MCL is an enforceable standard for drinking water.

Federal & State Government Resources

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Director: Rebecca Fry, PhD
Deputy Director: Fernando Pardo-Manuel de Villena, PhD
Funding provided by NIEHS grant #P42 ES031007

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