An excerpt from the New York State Department of Health website
Bacteria: A Definition
What are Coliforms?
"Coliforms are bacteria that are always present in the digestive
tracts of animals, including humans, and are found in their wastes.
They are also found in plant and soil material.Total Coliforms, Fecal
Coliforms, and E. Coli. The most basic test for bacterial contamination
of a water supply is the test for total coliform bacteria. Total coliform
counts give a general indication of the sanitary condition of a water supply.
A. Total coliforms include bacteria that are found in the soil,
in water that has been influenced by surface water, and in human or animal waste.
B. Fecal coliforms are the group of the total coliforms that are
considered to be present specifically in the gut and feces of warm-blooded animals.
Because the origins of fecal coliforms are more specific than the origins of the more
general total coliform group of bacteria, fecal coliforms are considered a more accurate
indication of animal or human waste than the total coliforms.
C. Escherichia coli (E. coli) is the major species in the fecal coliform
group. Of the five general groups of bacteria that comprise the total coliforms, only E. coli
is generally not found growing and reproducing in the environment. Consequently, E. coli is
considered to be the species of coliform bacteria that is the best indicator of fecal pollution
and the possible presence of pathogens. Are Coliform Bacteria Harmful?
Most coliform bacteria do not cause disease. However, some rare strains of E. coli, particularly
the strain 0157:H7, can cause serious illness. Recent outbreaks of disease caused by E. coli 0157:H7
have generated much public concern about this organism. E. coli 0157:H7 has been found in cattle,
chickens, pigs, and sheep. Most of the reported human cases have been due to eating under cooked hamburger.
Cases of E. coli 0157:H7 caused by contaminated drinking water supplies are rare. Coliform Testing
Testing for bacteria is the only reliable way to know if your water is safe. You cannot tell by the look,
taste, or smell of the water if disease-causing organisms are in it. The New York State Department of
Health recommends that well owners test their water for coliform bacteria at least once a year. If
you have experienced bacteria problems in the past, it is recommended that you test your well more
frequently. When Should I Test?
Late spring or early summer are the best times to test your well, since coliform contamination is most
likely to show up during wet weather. Whether your test results are positive or negative, understand
that the sample you collected is just a "snapshot" of your well’s water quality. The more samples you
have tested, the more confident you can be about the quality of the water you are drinking.What do the
If coliform bacteria are present in your drinking water, your risk of contracting a water-borne illness
is increased. Although total coliforms can come from sources other than fecal matter, a positive total
coliform sample should be considered an indication of pollution in your well. Positive fecal coliform
results, especially positive E. Coli results, should be considered indication of fecal pollution in
your well. What Should be done if Coliform Bacteria are Detected in a Well?
When coliforms have been detected, repairs or modifications of the water system may be required. Boiling
the water is advised until disinfection and retesting can confirm that contamination has been eliminated.
A defective well is often the cause when coliform bacteria are found in well water. What Kinds of Defects
can Allow Contamination?a missing or defective well cap - seals around wires, pipes, and where the cap
meets the casing may be cracked, letting in contaminants contaminant seepage through the well casing -
cracks or holes in the well casing allow water that has not been filtered through the soil to enter
the well. This seepage is common in the wells made of concrete, clay tile, or brick contaminant seeping
along the outside of the well casing - many older wells were not sealed with grout when they were
constructed well flooding - a common problem for wellheads located below the ground in frost pits that
frequently flood during wet weather. Long-Term Options for Dealing with Bacterial Contamination of a
WellConnecting to the regional public water system, if possible Inspecting wells for defects and
repairing them if possible Constructing a new well Installing continuous disinfection equipment Using
bottled water for drinking and food preparation."
For further information contact:
New York State Department of Health, Center for Environmental Health
at 1-800-458-1158 ext. 2-7650 or firstname.lastname@example.org.
New York State Department of Health. March 2005.
Coliform Bacteria in Drinking Water Supplies.
Retrieved July 11, 2007 from
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March 19, 2008