Technical Support Document for Ontario Drinking-water Quality Standards, Objectives and Guidelines
Escherichia coli (microbiological)
Escherichia coli should not be detected/present in any drinking water sample. Escherichia coli is a fecal coliform and can be detected using methods such as membrane filtration, presence/absence and MPN. Since Escherichia coli is present in fecal matter and prevalent in sewage, but is rapidly destroyed by chlorine, it is a strong indicator of recent fecal pollution. Contamination with sewage as shown by positive E-coli tests would strongly suggest presence of pathogenic bacteria and viruses, as well as more chlorine resistant pathogens such as Giardia and Cryptosporidium, which are much more difficult to detect.
Total Coliforms (microbiological)
The total coliform group consists of:
- all facultative anaerobic, Gram-negative, non-spore forming, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 35°C;
- many facultative anaerobic, Gram-negative, non-spore forming, rod-shaped bacteria that develop red colonies with a metallic (golden) sheen within 24 hours at 35°C on an Endo- type medium contain lactose; or,
- all bacteria possessing the enzyme β-galactosidase, which cleaves a chromogenic substrate
(e.g. ortho-nitrophenyl- β-galactopyranoside), resulting in a release of a chromogen (ortho- nitrophenol).
These definitions are not identical but refer to three groups that are roughly equivalent. All three groups contain various species of the genera Escherichia, Klebsiella, Enterobacte, Citrobacter, Serratia, and many others.
The presence of any total coliform bacteria in water leaving a treatment plant or in any treated water immediately post treatment signifies inadequate treatment and is unacceptable. Corrective action needs to be taken.
Heterotrophic Plate Count (microbiological)
Heterotrophic plate count (HPC) results give an indication of overall water quality in drinking- water systems. HPC results should be used as a tool for monitoring the overall quality of the water, both immediately post-treatment and in the distribution system. HPC results are not an indicator of water safety and, as such, should not be used as an indicator of potential adverse human health effects.
Sudden increases in HPC above normal baseline levels can indicate a change in raw water quality or a problem such as bacterial regrowth in the distribution system or plumbing. Steady increases in HPC over time indicate a gradual decline in raw water quality or in the condition of the system. Additionally, increases in disinfected systems can indicate a problem with drinking water treatment.