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Monitoring the bacteriological quality of drinking water is needed to control the presence of microorganisms that can cause illness or disease. Pathogenic microorganisms that occur in polluted water include protozoa, bacteria and enteric viruses. The most common disease this can cause is the gastrointestinal illness of diarrhea. Although gastrointestinal illness is usually non-life threatening in normal healthy adults, the risk of death increases among vulnerable groups such as infants, the elderly, and immunosuppressed individuals.
Since it is not practical (as tests are extremely costly) or technically feasible to monitor for all pathogens in drinking water, the microbiological quality of drinking water is evaluated based on indicator microorganisms, such as total coliforms and E.coli.
Coliform bacteria occur naturally in the environment and are not generally harmful. However, their presence suggests that other types of disease-causing organisms may exist in the drinking water.
Coliform bacteria have been selected as an indicator for the bacterial quality of drinking water in many nations. The presence of these bacteria in drinking water may signify the well is defective, or that there may be problems with the water treatment or the water distribution system.
Maximum acceptable concentration for drinking water has been set at no organisms detectable/100 mL.
Escherichia coli or E.coli is a type of coliform bacteria commonly found in the intestines of humans and warm-blooded animals. Most strains of E.coli do not cause illness in healthy humans and are actually beneficial to the synthesis of vitamins.
Some strains, however, cause cramps and diarrhea in humans. One particular strain named O157:H7 produces a powerful toxin that can cause severe illness. Health organizations across the world have selected E.coli as the most reliable indicator for the bacteriological quality of drinking water.
The presence of E.coli in water is a strong indication of recent sewage or animal waste contamination. Sewage may contain many other types of disease-causing organisms.
Presence of E.coli bacteria does not necessarily mean that your drinking water contains the strain of E.coli O157:H7. Health organizations do not believe it's necessary for a private well owner to test specifically for E.coli O157:H7 under normal circumstances. If E.coli O157:H7 is present in your well, it is highly likely that other strains of E.coli are also present. If a well has E.coli, regardless of strain, you should not drink the water unless it is effectively disinfected. Maximum acceptable concentration for E.coli for drinking water has been set at no organisms detectable/100 mL.