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Well Contaminants

Wells may be impacted by certain microbiological or chemical contaminants depending on the well location, well construction characteristics, area activities, and surface to groundwater geologic pathways. For example, wells in limestone geology, also known as "karst", may be more vulnerable to contamination from nearby surface activities. This is due to potential fissures in the limestone that can aid contaminants in traveling from surface to groundwater, especially during significant heavy rain events.


Bacteria is a common microbial contaminant that can be introduced into ground water through a combination of well construction characteristics, surface to groundwater geologic pathways, intense rain events, and various surface activities. A common test for bacteria is the "total coliform bacteria" test. See the testing information below to find a DEP regional office where a bacterial test kit can be purchased.

If you receive a positive test that shows total coliform bacteria present, this is an indication that you should not consume your water without boiling it first for 1 minute at a rolling boil. Boiled or bottled water should be used for drinking, cooking, food preparation, dishwashing, making ice and coffee, mixing baby formula and brushing teeth.

The National Sanitation Foundation (NSF) bacteria page has information on how you can treat for various microbiological microorganisms.


Viruses are very small microorganisms that can be introduced into the ground water. Since they are so small and test-specific, a positive total coliform test is assumed to indicate the possible presence of viruses.

Cryptosporidium and Giardia

If your well is suspected to have surface water infiltration, then you need to consider treating for both Cryptosporidium and Giardia.

Giardiasis is a waterborne disease caused by the protozoan Giardia lamblia that lives in the small intestine of warm-blooded mammals. Similarly, cryptosporidiosis is caused by Cryptosporidium parvum. Drinking water from a surface or surface water influenced source contaminated by Giardia cysts can cause infection. Giardianormally is not a problem with groundwater sources, unless they are under the direct influence of surface water.

Additional information on Giardia can be found in a pamphlet entitled " Cryptosporidium & Giardia...Are They in Your Drinking Water?"

Mechanical filtration is the most cost-effective way to remove Giardia cysts, although reverse osmosis and distillation are also effective. DEP recommends that consumers purchase a device that is in the NSF International listings for Giardia cyst removal. This information is included on NSF's treatment page.

Chemical Contaminants

Chemical contaminants can sometimes be introduced into ground water through various surface activities. At certain levels some of these chemical contaminants (such as iron and manganese) are not so much a health concern, but instead more of a nuisance. Other chemical contaminants may have health effects if they are consumed for many years.