What are coliform bacteria?

Coliform bacteria are a large assemblage of various species of bacteria that are linked together because of the ease of culturing as a single group.    They include both fecal coliform bacteria, or bacteria that are found naturally in the intestines of warm-blooded animals, and non-fecal coliform bacteria.  Fecal coliforms include both pathogenic, or disease-causing species, and non-pathogenic species.  The presence of fecal coliform bacteria indicates contamination of the waterbody by human and/or animal fecal material.

What is Escherichia coli?

Escherichia coli, commonly called E. coli, is one of the most common species of coliform bacteria.  It is a normal component of the large intestines in humans and other warm-blooded animals.  It is found in human sewage in high numbers.  E. coli is used as an indicator organism because it is easily cultured, and its presence in water in defined amounts indicates that sewage MAY be present.  If sewage is present in water, pathogenic or disease-causing organisms may also be present.

Why do we measure bacteria?

Typhoid and cholera epidemics in the mid-19th century led to the discovery that certain gastro-intestinal diseases of humans are transmitted via water.  The disease-causing organisms leave the infected individual via the feces, which can become discharged into surface waters.  They then in turn can be consumed by and infect users of the water.  These water-born diseases include typhoid, cholera, enteric fevers, and bacterial dysentery.  It is not feasible, however, to test waters for each possible type of disease-causing bacterium.  E. coli is used to indicate, on a statistical basis, the likelihood of contracting a disease by consuming or recreating in such waters.

What level of E. coli is acceptable?

The acceptable level of E. coli is determined by risk analysis based on statistics to protect human health.  Drinking water should have no E. coli after treatment.  E. coli levels at designated swimming beaches should not exceed 88 per 100 milliliter (mL) in any one sample, or exceed a three-sample geometric mean average over a 60-day period of 47/100mL.  Recreational waters that are not designated beaches should not have more than 406 E. coli/100mL in any one sample, or more than 126/100mL in a 60-day, three-sample geometric mean average.  Occasional higher numbers are not unusual, particularly after storm events and where urban or agricultural runoff occurs.  These levels are generally not considered unsafe unless investigation indicates the source to be sewage.

Can I drink my lake water?

Because E. coli are present in all warm-blooded animals, including ducks, beaver, and sea gulls, it is highly unlikely that any lake will have zero E. coli without treatment.  Even with no E. coli, lake water is still not safe to be used directly as a source of drinking water.  Without adequate treatment there can be no guarantee concerning the safety of the water.

Does E. Coli cause swimmers’ ear or ear infections?

No.  There are a number of illnesses, particularly related to the eyes, ears, nose, and throat, which may use water as the medium of transmission but in which the disease-causing organism does not necessarily pass through the feces of the infected individual.  Just as you may catch a cold by being in the same room as an infected individual, you may catch an ear infection by swimming in a lake with an infected individual.  This can occur, even though no sewage is being discharged into the lake.  Fortunately, these organisms generally do not survive very long in the water.