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Total Coliform Laboratory Analysis of Drinking Water

Coliform bacteria, found in the intestines of warm-blooded animals including humans, are indicators of water contamination. They are generally not harmful by themselves, but their presence implies contamination by fecal matter, which could contain other organisms capable of causing illnesses ranging from mild diarrhea and cramps to kidney failure in immune-compromised groups such as infants and the elderly. Public departments of health mandate regular testing of water used for drinking and for swimming and other recreational activities. There are four approved laboratory tests for coliform bacteria.

  1. Presence-Absence Test

    • The presence-absence test is sensitive, economical and efficient, the typical test time being less than a minute for a 100-mL sample. However, this test does not determine how many coliform bacteria are present: It indicates only whether they are present. It may produce false-positive results.

    Membrane Filter Test

    • In the membrane filter test, the water sample is filtered through a membrane that retains the bacteria, which are then transferred to a growth medium for identification and counting. This method is not useful in highly turbid water because the particulates interfere with bacterial growth. It cannot detect bacteria that have been temporarily suppressed by chlorination but have the potential to redevelop.

    Multiple Tube Fermentation Test

    • In the multiple tube fermentation test, water to be tested is first diluted and then put into a number of tubes: each tube contains a substance specific to a certain type of coliform bacteria. The presence of bacteria causes a color change in the testing medium. Only a statistical indication, called the most probable number, is possible. Compared to the membrane filter test, the multiple tube test is less precise and takes more time. Therefore, it is used only when membrane filter results are not reliable because of turbidity or when confirmation is required.

    MMO-MUG Test

    • The MMO-MUG test, named after the detecting substances used, was developed about 1990 and is the latest of the approved methods. The water sample is exposed to the MMO-MUG medium for about 24 hours and if the color of the medium changes to a certain shade of yellow, coliforms are confirmed.

    Laws and Regulations

    • Generally, regulations do not allow any coliform bacteria in drinking water. Swimming in water with up to about 70 coliforms per 100 mL is allowed because it is recognized that recreational areas are also wildlife habitats. Regulations in the United States comply with the Clean Water Act, promulgated in 1972 and amended in 1977. The Environmental Protection Agency is the federal agency responsible for drinking water standards. There are 18 national primary drinking water regulations. The World Health Organization has also prepared a series of guidelines on drinking water quality.

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