Question: Is there a difference between total microbe test and a total coliform test. What do the following results mean as far as safe drinking water is concerned, (5-10)(10-20)(400-500) (800-1000) Colony forming units(CFUs) of aerobic bacteria?
Answer: There is a difference between total microbes test and total coliform test. The former is a non-specific test for everything including the coliforms (if they are present). This test is commonly referred to as Heterotrophic Plate Count (HPC) or Total Aerobic Plate Count. HPC does not give an indication of the types of organisms present or their sources. The total coliform test is designed to detect bacteria belonging to the coliform group.
I am not sure whether the results above were CFUs per litre or per 100 mL. Assuming these were per 100 mL of water the first set of results would be considered insignificant provided coliforms were not present. The second two sets of results suggests the water is either not properly treated or is getting contaminated after treatment.
Below are the Health Canada Microbiological Guidelines for Canadian Drinking Water Quality.
Guidelines for microbiological parameters
Currently available detection methods do not allow for the routine analysis of all microorganisms that could be present in inadequately treated drinking water. Instead, microbiological quality is determined by testing drinking water for Escherichia coli, a bacterium that is always present in the intestines of humans and other animals and whose presence in drinking water would indicate faecal contamination of the water.
The maximum acceptable concentration (MAC) of Escherichia coli in public, semi-public, and private drinking water systems is none detectable per 100 mL.
Testing for E. coli should be carried out in all drinking water systems. The number, frequency, and location of samples for E. coli testing will vary according to the type and size of the system and jurisdictional requirements.
The MAC of total coliforms in water leaving a treatment plant in a public system and throughout semi-public and private supply systems is none detectable per 100 mL.
For distribution systems in public supplies where fewer than 10 samples are collected in a given sampling period, no sample should contain total coliform bacteria. In distribution systems where greater than 10 samples are collected in a given sampling period, no consecutive samples from the same site or not more than 10% of samples should show the presence of total coliform bacteria.
Testing for total coliforms should be carried out in all drinking water systems. The number, frequency, and location of samples for total coliform testing will vary according to the type and size of the system and jurisdictional requirements.
Heterotrophic plate count
No MAC is specified for heterotrophic plate count (HPC) bacteria in water supplied by public, semipublic, or private drinking water systems. Instead, increases in HPC concentrations above baseline levels are considered undesirable.
No MAC for current or emerging bacterial waterborne pathogens has been established. Current bacterial waterborne pathogens include those that have been previously linked to gastrointestinal illness in human populations. Emerging bacterial waterborne pathogens include, but are not limited to, Legionella, Mycobacterium avium complex, Aeromonas hydrophila, and Helicobacter pylori.
Although Giardia and Cryptosporidium can be responsible for severe and, in some cases, fatal gastrointestinal illness, it is not possible to establish MACs for these protozoa in drinking water at this time. Routine methods available for the detection of cysts and oocysts suffer from low recovery rates and do not provide any information on their viability or human infectivity. Nevertheless, until better monitoring data and information on the viability and infectivity of cysts and oocysts present in drinking water are available, measures should be implemented to reduce the risk of illness as much as possible. If the presence of viable, human-infectious cysts or oocysts is known or suspected in source waters, or if Giardia or Cryptosporidium has been responsible for past waterborne outbreaks in a community, a treatment and distribution regime and a watershed or wellhead protection plan (where feasible) or other measures known to reduce the risk of illness should be implemented. Treatment technologies in place should achieve at least a 3-log reduction in and/or inactivation of cysts and oocysts, unless source water quality requires a greater log reduction and/or inactivation.
Although enteric viruses can be responsible for severe and, in some cases, fatal illnesses, it is not possible to establish MACs for enteric viruses in drinking water at this time. Treatment technologies and watershed or wellhead protection measures known to reduce the risk of waterborne outbreaks should be implemented and maintained if source water is subject to faecal contamination or if enteric viruses have been responsible for past waterborne outbreaks. Where treatment is required, treatment technologies should achieve at least a 4-log reduction and/or inactivation of viruses.
For more details on Canadian Guidelines for drinking water click Guidelines for Canadian Drinking Water Quality.