E. coli is a type of fecal coliform bacteria commonly found in the intestines of animals and humans. E. coli is short for Escherichia coli. The presence of E. coli in water is a strong indication of recent sewage or animal waste contamination. Sewage may contain many types of disease-causing organisms.


Fecal coliform and E. coli are bacteria whose presence indicates that the water may be contaminated with human or animal wastes. Disease-causing microbes (pathogens) in these wastes can cause diarrhea, cramps, nausea, headaches, or other symptoms. These pathogens may pose a special health risk for infants, young children, and people with severely compromised immune systems.

Rivers are an important source of water for agricultural use and are popular for recreational activities. Bacterial contamination of these water bodies may pose a risk to human, animal, and ecosystem health.

E. coli comes from human and animal wastes. During rainfalls, snow melts, or other types of precipitation, E. coli may be washed into creeks, rivers, streams, lakes, or ground water. When these waters are used as sources of drinking water and the water is not treated or inadequately treated, E. coli may end up in drinking water.

The presence of E. coli in a water supply suggests that the water may have been recently contaminated with the fecal material of humans or animals. This can be associated with improper or inadequate sewage treatment, overflow of municipal sewage systems, urban runoff, or other point and non-point sources of bacteria, such as livestock operations. Not only does this represent a potential health risk, but it may also indicate concurrent contamination with other waterborne pollutant.

Water can be treated using chlorine, ultra-violet light, or ozone, all of which act to kill or inactivate E. coli.

If you draw water from a private well, you can contact your local health department to obtain information on how to have your well tested for total coliforms and E. coli contamination. If your well tests positive for E. coli, there are several steps that you should take:


If the contamination is a recurring problem, you should investigate the feasibility of drilling a new well or install a point-of-entry disinfection unit, which can use chlorine, ultraviolet light, or ozone.


In general, SEAWA has established Water Quality Objectives for E.coli that meet recreational guidelines – no single measurement is to exceed a count of 100 E.coli per 100 mL.

In general, rating (condition) of the E.coli indicator is based on the number of times that recorded measurements over a one year period “exceeded” the Water Quality Objective (WQO) at that location.