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This article gives advice on testing water for bacterial contamination using the total coliform test.
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If water "fails" a T-coli test, further testing is needed. Because not all coliform bacteria are cause for "failing" a water potability test, if a water test result discloses high or excessive T-coli alone, what we can conclude is that further investigation is needed.
If the water test passes a T-coli test as not detected, absent, or below your community's acceptable minimum level, the water is considered safe to drink insofar as bacterial contamination is concerned. Of course other contaminants (chemicals, for example) could still be present in such a water sample.
Escherichia coli (EC or E-coli) bacteria tests in water indicate the presence of (or depending on the test performed, the count or level of colony forming units of) Escherichia coli.
If water "faIls" an E-coli test, the water is not safe to drink. Escherichia coli is a specific indicator of the presence of humanh or animal fecal waste contamiantion of the water supply, a water test which detects an unacceptable level of Escherichia coli is unsafe to drink. The source of contamination needs to be found and corrected or if this is not possible, an appropriate water treatment system is installed.
As we suggested above for T-coli, if the water test passes an E-coli test as not detected, absent, or below your community's acceptable minimum level, the water is considered safe to drink insofar as bacterial contamination is concerned. Furthermore, T-coli may be present and E-coli absent and the water test may be considered acceptable. However in our OPINION, a high T-coli water test
Of course other contaminants (chemicals, for example) could still be present in such a water sample.
HPC heterotrophic plate count in water test results: aerobic and facultative aerobic bacteria are both detected by the HPC count.
The HPC count is not part of most basic water potability tests. You may order this test, for example, as part of diagnosing a known or suspected problem, or to help check for growth of microbial contaminants in treated water. HPC or the heterotrophic plate count, along with total coliforms (T-coli) and Escherichia coliform (E-coli) counts are used to indicate the level of microbiological contamiantion of water tests for potability.
For more information about the use of HPC testing of drinking water see this World Health Organization paper: The History and Use of HPC in Drinking-Water Quality Management (web searhc 02/10/2011, original source http://www.who.int/water_sanitation_health/dwq/HPC3.pdf)
A basic water "bacteria test" may or may not be equally sensitive to all three of these data, and not all water tests or water test labs report all three of these individual measures.
Watch out: even if your water sample passes a coliform test, bacteria test, or T-coli or E-coli test, that does not guarantee that there are no chemical contaminants in the water supply.
Not all water bacteria tests are the same. See these articles about water tests for bacterial or microbial contamination:
Will Coliform bacteria in water make you sick?
When we find Coliform bacteria in your drinking water sample, as stated above, it simply indicates that the source is, or recently has been compromised by surface water. We're not so concerned about the Coliform bacteria themselves, but the "red flag" if you will, is that we don't know what else may have gotten in your drinking water system via the same route that the Coliform bacteria entered. Some types of bad microbes we don't want you to ingest, for example, would be Klebsiella, Shigella, Cryptosporidium, Giardia, or Salmonella, just to name a pesky few!
Most drilled wells are free from Coliform bacteria, but many dug wells contain Coliform. This is not surprising, since dug wells are a surface water source, which means it is above the bedrock layer. Dug wells, can be an excellent source of drinking water, but extra care should be taken to be sure there is adequate separation from the well with respect to pets, farm animals, and runoff.
If you have a dug well, the volume and taste are fine, but it keeps getting Coliform bacteria, then a viable and effective option may be to install an ultraviolet disinfection system, which kills the bacteria and other microbes by separating, or denaturing the DNA or RNA of their cells. This works well because it doesn't change the chemistry of the water like some other disinfection methods, such as chlorination.
However any water treatment system requires care and monitoring, lest you think it's working when it's not. Further, the presence of surface water in your water supply might mean that other surface contaminants, such as chemicals, are also present. If this is the case, a UV-light is not going to remove them. This is why further testing of your water may be in order before deciding just what water treatment system should be installed.
Finally, if Total Coliform bacteria is found in a drinking water sample, then the sample is also checked for a type of fecal Coliform bacteria, which is always Escherichia coli, or E. coli. The presence of E. coli may mean a septic or leach field infiltration, or in a dug well, it just may be a squirrel or field mouse that tried to make his home in your well! We'll cover well disinfection in another session.
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