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Fecal Coliform Bacteria in Water

coliform colony in petri dish

What are Fecal Coliform Bacteria?

Coliform bacteria are a collection of relatively harmless microorganisms that live in large numbers in the intestines of humans and warm- and cold-blooded animals. They aid in the digestion of food.  A specific subgroup of this collection is the fecal coliform bacteria, the most common member being Escherichia coli.  These organisms may be separated from the total coliform group by their ability to grow at elevated temperatures and are associated only with the fecal material of warm-blooded animals. 

The fecal coliform group includes all of the rod-shaped bacteria that are non-spore forming, Gram-Negative, lactose-fermenting in 24 hours at 44.5 °C, and which can grow with or without oxygen. 

Fecal coliform by themselves are usually not pathogenic; they are indicator organisms, which means they may indicate the presence of other pathogenic bacteria. Pathogens are typically present in such small amounts that it is impractical to monitor them directly.

Note - Some strains of Escherichia coli, which are a type of fecal coliform, can cause intestinal illness. One such strain is E. coli O157:H7, which is found in the digestive tract of cattle.

Environmental Impact

The presence of fecal coliform bacteria in aquatic environments indicates that the water has been contaminated with the fecal material of humans or other animals.  At the time this occurred, the source water may have been contaminated by pathogens or disease-producing bacteria or viruses which can also exist in fecal material. 

Some waterborne pathogenic diseases include typhoid fever, viral and bacterial gastroenteritis, and hepatitis A. The presence of fecal contamination is an indicator that a potential health risk exists for individuals exposed to this water. Fecal coliform bacteria may occur in ambient water as a result of the overflow of domestic sewage or nonpoint sources of human and animal waste.

Significance: Fecal Coliform bacteria indicate the presence of sewage contamination of a waterway and the possible presence of other pathogenic organisms.

Bacteria are single-celled organisms that can only be seen with the aid of a very powerful microscope. Bacteria can be found everywhere - in air, water, and soil, even in and on your own body. They can benefit us by recycling wastes, helping nitrogen-fixing plants to grow, and by making certain types of food. They may harm us by causing diseases and food spoilage. Of environmental concern are the many types of coliform bacteria. Fecal coliform bacteria are a group of bacteria that are passed through the fecal excrement of humans, livestock, and wildlife. 

Bacteria reproduce rapidly if conditions are right for growth. Most bacteria grow best in dark, warm, moist environments with food. Some bacteria form colonies as they multiply which may grow large enough to be seen. By growing and counting colonies of fecal coliform bacteria from a sample of stream water, we can determine approximately how many bacteria were originally present.

Fecal coliform bacteria can enter rivers through the direct discharge of waste from mammals and birds, from agricultural and storm runoff, and from untreated human sewage. Individual home septic tanks can become overloaded during the rainy season and allow untreated human wastes to flow into drainage ditches and nearby waters. Agricultural practices such as allowing animal wastes to wash into nearby streams during the rainy season, spreading manure and fertilizer on fields during rainy periods, and allowing livestock watering in streams, can all contribute to fecal coliform contamination.

At the time this occurs, the source water may be contaminated by pathogens or disease-producing bacteria or viruses, which can also exist in fecal material. The presence of fecal coliform tends to affect humans more than it does aquatic creatures, though not exclusively. While these bacteria do not directly cause disease, high quantities of fecal coliform bacteria suggest the presence of disease-causing agents. During high rainfall periods, sewers can become overloaded and overflow, bypassing treatment. As it discharges to a nearby stream or river, untreated sewage enters the river system. Runoff from roads, parking lots, and yards can carry animal wastes to streams through storm sewers.

Fecal Coliform Testing

Membrane filtration is the method of choice for the analysis of fecal coliforms in water. Samples to be tested are passed through a membrane filter of a particular pore size (generally 0.45 micron). The microorganisms present in the water remain on the filter surface. When the filter is placed in a sterile petri dish and saturated with an appropriate medium, growth of the desired organisms is encouraged, while that of other organisms is suppressed. Each cell develops into a separate colony, which can be counted directly, and the results calculated as microbial density. Sample volumes of 1 ml and 10 ml will be used for the water testing, with the goal of achieving a final desirable colony density range of 20-60 colonies/filter. Contaminated sources may require dilution to achieve a "countable" membrane.

A 100 ml volume of a water sample is drawn through a membrane filter (45 micron pore size) through the use of a vacuum pump. The filter is placed on a petri dish containing M-FC agar (a bacterial nutrient) and incubated for 24 hours at 44.50 °C. This elevated temperature heat-shocks non-fecal bacteria and suppresses their growth. As the fecal coliform colonies grow, they produce an acid (by fermenting lactose) that reacts with the aniline dye in the agar, thus giving the colonies their blue color, making them easier to count.

The new US EPA coliform rule requires major monitoring changes by the drinking water industry. The testing requirements for drinking water are markedly increased. Not only is the number of routine coliform tests increased, especially for the smaller utilities, but a new regulation requires automatic repeat-testing from all sites that show a total coliform positive result.

Fecal Coliform Bacteria in Streams

Why Is It Important?

Fecal coliform bacteria are microscopic organisms that live in the intestines of warm-blooded animals. They also live in the waste material, or feces, excreted from the intestinal tract. When fecal coliform bacteria are present in high numbers in a water sample, it means that the water has received fecal matter from one source or another. Although not necessarily agents of disease, fecal coliform bacteria may indicate the presence of disease-carrying organisms, which live in the same environment as the fecal coliform bacteria.

Swimming in waters with high levels of fecal coliform bacteria increases the chance of developing illness (fever, nausea, or stomach cramps) from pathogens entering the body through the mouth, nose, ears, or cuts in the skin. Diseases and illnesses that can be contracted in water with high fecal coliform counts include typhoid fever, hepatitis, gastroenteritis, dysentery, and ear infections. Fecal coliform, like other bacteria, can usually be killed by boiling water or by treating the water with chlorine. Washing thoroughly with soap after contact with contaminated water can also help prevent infections.

Untreated fecal material adds excess organic material to the water which decays, depleting the water of oxygen. This lowered oxygen may kill fish and other aquatic life. Reduction of fecal coliform in wastewater treatment may require the use of chlorine and other disinfectant chemicals. Such treatment is designed to kill the fecal coliform and disease-causing bacteria but will also kill bacteria essential to the proper balance of the aquatic environment, endangering the survival of species dependent on those benign bacteria; the disinfection agent and/or disinfection byproducts may also threaten other aquatic organisms.

Reasons for Natural Variation

Unlike the other conventional water quality parameters, fecal coliform bacteria are living organisms. They do not simply mix with the water and float straight downstream. Instead, they multiply quickly when conditions are favorable for growth, or die in large numbers when conditions are not. Because bacterial concentrations are dependent on specific conditions for growth, and these conditions change quickly, fecal coliform bacteria counts are not easy to predict. For example, although winter rains may wash more fecal matter from urban areas into a stream, cool water temperatures may cause a major die-off because of unfavorable environmental conditions. Exposure to sunlight (with its ultraviolet disinfection properties) may have the same effect, even in the warmer water of summertime.

Expected Impact of Pollution

The primary sources of fecal coliform bacteria to freshwater are wastewater treatment plant discharges, failing septic systems, and animal waste. Bacteria levels do not necessarily decrease as a watershed develops from rural to urban. Instead, urbanization usually generates new sources of bacteria. Farm animal manure and septic systems are replaced by domestic pets and leaking sanitary sewers. In fact, stormwater runoff in urbanized areas has been found to be surprisingly high in fecal coliform bacteria concentrations. The presence of old, disintegrating storm and sanitary sewers, misplaced sewer pipes, and good breeding conditions are common explanations for the high levels sometimes measured in urban areas. 

EPA Standard for E. Coli

Fecal coliform concentrations are reported in units of the number of bacterial colonies per 100 mL of sample water (#/100 mL). The current US EPA recommendations for body-contact of recreational water is fewer than 200 colonies/100 mL; for fishing and boating, fewer than 1000 colonies/100 mL; and for domestic water supply, for treatment, fewer than 2000 colonies/100 mL. The drinking water standard is less than 1 colony of Total Coliform Bacteria/ 100 ml with E. coli absent.

Graph of fecal coliform test results
The original graphical analysis prior to the development of our new Water Quality Index Calculator for the Parameter Fecal Coliform.

Check out our Water Quality Index Calculator for Surface Waters

Wastewater and Septic System Effluent

Fecal coliform is present in human waste, so the fecal bacteria go down the drains in our houses and businesses, and can enter streams from illegal or leaky sanitary sewer connections, poorly functioning septic systems, and poorly functioning wastewater treatment plant (WWTPs) effluent.

Animal Waste

A significant amount of fecal coliform is released in the wastes produced by animals. This can be a serious problem in waters near cattle feedlots, hog farms, dairies, and barnyards that have poor animal-keeping practices such as improper containment of animal waste. In urban areas, fecal coliform can be contributed to surface water by dog, cat, raccoon, and human waste when it is carried into storm drains, creeks, and lakes during storms.

Sediment Load

High amounts of sediment are often related to high concentrations of pathogenic bacteria because the bacteria can attach to sediment particles. Fast-running water can carry more sediment, so higher levels of bacteria can occur during high runoff events. Bacteria are much more abundant on soil particles than in water.


Bacteria grow faster at higher temperatures. The growth rate slows drastically at very low temperatures.


High levels of nutrients can increase the growth rate of bacteria; sewage is rich in such nutrients.

Additional Resources