Microorganisms, Bacteria and Viruses

Microbiological contamination of water has long been a concern to the public. From the 1920's-1960's, the bacillus which causes typhoid fever was considered a major problem in the water supply (1). Once it was eradicated, new microbes were present to take its place. In parts of the United States, concern is inreasing due to outbreaks of coliform bacteria, giardiasis, cryptosporidiosis, and hepatitis A (1,2,3). Some of these are bacteria, while others are viruses or protozoa. If you are on a public water supply system, and you are concerned about the possibility of microbial contamination, contact your water company. If you use a private water  supply, have your water tested by a reputable lab. Treatments do exist for microbial contamination, but, it is important to know what is present before treatment is begun.

Coliform Bacteria

Coliform bacteria  live in soil or vegetation and in the gastrointestinal tract of animals. Coliforms enter water supplies from the direct disposal of waste into streams or lakes, or from runoff from wooded areas, pastures, feedlots, septic tanks, and sewage plants into streams or groundwater. In addition, coliforms can enter an individual house via backflow of water from a contaminated source, carbon filters, or leaking well caps that allow dirt and dead organisms to fall into the water (2).

Coliforms are not a single type of bacteria, but a grouping of bacteria that includes many strains, such as E. coli. They are ubiquitous in nature, and many types are harmless. Therefore, it is not definitive that coliform bacteria will cause sickness. Many variables such as the specific type of bacteria present, and your own immune system's effectiveness will determine if you will get sick. In fact, many people become immune to bacteria that is present in their own water (2). Guests on the other hand, may not have developed an immunity to the water and may experience some gastrointestinal distress such as diarrhea or gastroenteritis (2).

Total coliforms are the standard by which microbial contamination is measured. Coliforms will be one of the first bacteria present in the water should contamination occur, and they will be in much larger quantities than some pathogenic microbes that may be present. Therefore, coliforms act as indicators of possible contamination. The presence of coliform bacteria does not necessarily mean that pathogenic microbes are also present. However, if large coliform quantities are detected, the presence of other microbes should be checked for. If you are a private water consumer and concerned about your water supply, you can obtain more information about protecting your private water supply from the EPA. Generally, testing is done once a year.  However it may also be wise to test the water for the following reasons:

  1. A new well or pump has been installed
  2. An old well or pipe has been repaired or replaced
  3. Family or guests are have reoccurring gastrointestinal distress
  4. An infant is living in the home
  5. A new home is being purchased, and the quality of water needs to be determined
  6. The effectiveness of a water treatment system needs to be tested
  7. The water has had a change in taste, color or odor (2)

Testing of your water can be done by a local testing laboratory, or by a county or state health laboratory.

If your water is found to be contaminated, the best treatment is generally disinfection or filtration. Other options involve UV irradiation and ozonation. A water professional can help you select the best treatment (2).

If you would like to learn more about coliform bacteria, The National Groundwater Association is a good place to start.

Giardia Lamblia

Giardia has become more prevalent in the past few years as a waterborne disease, and a few large outbreaks that have occurred in the U.S. (3). Giardia are flagellated protozoa that are parasitic in the intestines of humans and animals (4). They have two stages, one of which is a cyst form that can be ingested from contaminated water. Once the cyst enters the stomach, the organism is released into the gastrointestinal tract where it will adhere to the intestinal wall. Eventually the protozoa will move into the large intestine where they encyst again and are excreted in the feces and back into the environment (4).

Once in the body, the giardia causes giardiasis, a disease characterized by symptoms such as diarrhea, abdominal cramps, nausea, weight loss, and general gastrointestinal distress. These symptoms last for about a week, however some people can undergo a more chronic infection with similar symptoms and an even greater degree of weight loss (3). Giardiasis is rarely fatal (6), and can be treated medicinally by quinacrine, metronidazole, and furazolidone (3).

Giardia enters the water supply via contamination by fecal material. The fecal material can enter the water from:

Once in these water bodies, unsuspecting hikers or campers may drink infected water, exposing themselves to the cysts. Water from these lakes or streams may also be transported to municipal water supplies. If the municipal system uses sand filtration in addition to chlorination, the cysts should be removed. If chlorination is used without filtration, the chance for a giardia infection increases (4). It is estimated that 20-65 million Americans are at risk due to this lack of filtration of surface water (3,5). It has been suggested that 40-45% of giardia cases are associated with exposure to unfiltered water (4). Other sources of exposure include unsanitary conditions at day care facilities, exposure while traveling in developing countries, hikers or campers drinking infected surface water, and sexual practices involving fecal exposure (4).

If water is contaminated with giardia, it is possible to kill the cysts by simply boiling the water. If you are on a public water system, a notice will be sent out should coliform and giardia be present at unsafe levels. People on private water systems should not be concerned as most giardia is from untreated surface water; however there is a possibility that sewage lines from a septic tank may infect your water. Contamination from livestock waste may also be of some concern. If you are in doubt, it is possible to have your well water tested for bacteria and protozoa by laboratories in your area (2).


Cryptosporidium parvum is a protozoan parasite that causes cryptosporidiosis, which has gained notoriety in the past five years. In 1993, over 400,000 people in Milwaukee, Wisconsin became ill with it after drinking contaminated water (6). Since this outbreak, there has been a greater impetus to remove the cryptosporidium from municipal water supplies.

Cryptosporidium is spread by the transmission of oocysts   via drinking water  which has been contaminated with infected fecal material.  Oocysts from humans are infective to humans and many other mammals, and many animals act as reservoirs of oocysts which can infect humans. Once inside of its host, the oocyst breaks, releasing four movable spores that attach to the walls of the gastrointestinal tract, and eventually form oocysts again that can be excreted (4). Symptoms occur 2 to 10 days after infection (6). These symptoms include diarrhea, headache, abdominal cramps, nausea, vomiting, and a low fever. There is no treatment against the protozoa, although it is possible to treat the symptoms. After about 1-2 weeks, the symptoms subside as the immune system stops the infection. However, for persons with a compromised immune system such as infants, seniors, those with AIDS, or transplantees, cryptosporidiosis may become life threatening (4,6).

Cryptosporidium infected fecal material enters the water supply either from cross contamination of sewage lines with water lines, or surface water infected with contaminated animal waste. Water treatment processes that utilize coagulation, sedimentation, filtration and chlorination may remove it. However, due to its small size and its resistance to chlorination, these treatments may not work (4). If cryptosporidium is a concern in your area, boiling your water for at least one minute is an effective way to kill it (6).

As with giardia, if you are on a public system you should receive a notice if cryptosporidium levels have increased. However, if you are on a private system using a well, contamination may occur from a leaking or improperly placed septic tank, or animal waste, so it may be a good idea to test for total coliforms. If the amount of coliforms are low, then more than likely cryptosporidium is not a problem (2).

If you would like to obtain more information about cryptosporidium, including how to prevent it, the website at the Centers for Disease Control will be able to help you out.

Hepatitis A:

Hepatitis A is an enteric virus that is very small. It can be transferred through contaminated water, causing outbreaks (5). The virus is excreted by a person carrying it, and if the sewage contaminates the water supply, then the virus is carried in the water until it is consumed by a host. Symptoms such as an inflamed liver, accompanied by lassitude, anorexia, weakness, nausea, fever and jaundice are common. A mild case may only require a week or two of rest, while a severe case can result in liver damage and possible death (4). Generally, water systems utilize chlorination, preceded by coagulation, flocculation, settling and filtration to remove the virus (5). Boiling your water will also inactivate the virus (3,6). Should you be using a private water system, you may want to check your well water for coliform bacteria. If there is a large amount of bacteria present, there is most likely contamination from sewage, and the water needs to be treated (2).


Helminths are parasitic worms that grow and multiply in sewage and wet soil (5). They enter the body by burrowing through the skin, or by ingestion of the worm in one of its many lifecycle phases (7). The eggs as well as the adult and larval forms of the worms are large enough to be trapped during conventional water treatments, so they tend not be a problem in water systems (7). In addition, most of these helminths are not waterborne, so chances of infection are minimized (4). Drinking water is usually not tested for these, as they are not considered to be much of an issue in the United States; they are more prevalent in developing countries (4).


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  1. Craun, G.F., Waterborne Disease in the United States. 1986. CRC Press, Inc. Boca Raton, FL.
  2. National Groundwater Association. 601 Dempsey Road, Westerville, Ohio. 614-898-7791. http://www.h2O-ngwa.org/pubaff/bacq_a.html
  3. Juranek, D. Giardiasis. Division of Parasite Diseases, Centers for Disease Control and Prevention, Atlanta GA.
  4. Guidelines for Drinking Water Quality. 2nd edition, Volume 2. 1996. WHO, Austria.
  5. John DeZyane, P.E. Handbook of Drinking Water Quality. 1990. Van Nostrand Reinhold, NY.
  6. Drinking Water and Health.1977. National Academy of Sciences, Washington D.C. 1977.

URL References:

  1. Bacteria and Drinking Water Supplied by Private Wells, Frequently Asked Questions. (no date), National Groundwater Association: URL: http://www.h2O-ngwa.org/pubaff/bacq_a.html
  2. Juranek, D.D. Cryptosporidiosis: Sources of Infection and Guidleines for Prevention. Clinical Infectious Diseases, 1995; 21(suppl1)S57-61. Located at Centers for Disease Control and Prevention, URL: http://www.cdc.gov/ncidod/diseases/crypto/sources.htm
  3. EPA, OGWDW, Protecting Private Drinking Water Supplies, September 3, 1997. URL: http://www.epa.gov/OGWDW/wot/whatdo.html

This page was prepared by S.L. Keyser, June 1997, UCD EXTOXNET FAQ Team.
Revised by B.T. Johnson on October 22, 1997.