Water Testing - Bacteria
Determining the bacterial quality of drinking water is the single most important water quality test. Why? Because one glass of water containing just a few disease organisms can cause illness. When minimal exposure creates an immediate health risk, that contaminant is known as an acute contaminant. Bacterial contaminants such as E. coli and fecal coliform in drinking water represent an acute health risk. In contrast, meaningful health risk from most chemical contaminants, such as arsenic, radon, or benzene, requires a long period of exposure. Consequently, these contaminants are considered chronic.
The total coliform test is the starting point for determining the biological quality of drinking water. This test is performed frequently because of the acute risk that disease-causing organisms pose to the users of that water supply.
Total Coliform Test
Coliform bacteria which are found in large numbers living beside pathogenic microorganisms in the intestinal tracts of warm-blooded animals. Masses of coliform bacteria are discharged from the intestinal tract with these animals' feces. If sewage enters water, the coliform bacteria in the sewage will be carried along and will survive in the water for long periods of time. Thus, the presence of coliform bacteria provides evidence that water has been polluted with sewage, and also indicates the possible presence of pathogenic microbes. The total coliform test remains the most commonly used standard for determining the bacterial quality of drinking water in the US and the world.
This is a subset of the total coliform group. Fecal coliform bacteria generally originate in the intestines of mammals. They have a relatively short life span compared to other coliform bacteria. Their presence could be related to improper disposal of sanitary waste. Immediate public notice and a boil order to the users (within 24 hours) are required due to the higher likelihood of disease organisms also being present in water.
Escherichia coli (E. coli)
This is a species within the fecal coliform group. E. coli originate only in the intestines of animals including humans. As with other fecal coliform, they have a relatively short life span compared to nonfecal coliform bacteria. Their presence indicates a strong likelihood that human or animal wastes are entering the water system. Immediate public notice and a boil order (within 24 hours) are required due to a higher likelihood of disease organisms also being present in the water.
Heterotrophic Plate Count (HPC)
The heterotrophic plate count (HPC), formerly known as the standard plate count, is a procedure for estimating the number of live heterotrophic bacteria (requiring organic compounds of carbon and nitrogen for nourishment) in water. (HPC) is a microbial method that uses colony formation on culture media to approximate the levels of heterotrophic flora. HPC does not, however, give an indication of the types of organisms present or their sources. Most bacteria, including many of the bacteria associated with drinking water systems, are heterotrophs. This test can provide useful information about water quality and supporting data on the significance of coliform test results.