Well water and health

Some drinking water contaminants are harmful to human health but do not cause any noticeable changes to the taste, smell, or color of the water.54

Private well owners must take special precautions to ensure the safety and maintenance of their drinking water supplies.5  

Some contaminants in well water, like bacteria and nitrates, can cause short-term illnesses (such as gastrointestinal upset, diarrhea, nausea) and may be especially dangerous for certain high-risk populations such as small children, pregnant women, elderly, or individuals with a compromised immune system.7

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

Contact with chemicals that are genotoxic carcinogens (chemicals that can cause damage to DNA) will have some degree of risk at any level of exposure.

The degree of risk from contact with contaminants in drinking water depends upon the length of time that you are in contact with the contaminant and the amount of the contaminant to which you are exposed.  The effects of exposure to any substance also depend upon how you are exposed (such as through breathing, drinking, or skin contact), your individual susceptibility to a contaminant, and whether other chemicals are present.


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

Primary contaminants are substances that can cause changes to your health if you drink them in levels that exceed the regulatory standards for a long period of time.11

Secondary contaminants are substances that can be a nuisance to homeowners because they alter the taste and smell of the water or cause staining of household fixtures.  Secondary contaminants not likely to cause adverse impacts to health and are not enforceable in public drinking water supplies.11

The US EPA regulates contaminants in public drinking water supplies and establishes standards for drinking water quality.  The US EPA has established Maximum Contaminant Levels (MCL) or required treatment processes for all primary contaminants in drinking water.  In addition to establishing MCLs, the US EPA has also established Maximum Contaminant Level Goals (MCLG) for these contaminants. MCLGs provide a standard  below which there are no known or expected health risks.  MCLGs allow for a margin of safety and are non-enforceable public health goals.

Additional information about drinking water standards


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.

Additional information about sources of contamination


This project was funded by an ARRA supplement from the National Institute of Environmental Health Sciences (#P42ES005948) 2009-2011.