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What is Indicator Microorganism?

          The microorganisms in water shows that it is polluted. We can determine the type and the level of the pollution by conducting several tests. Various indicator microorganisms are used to test for faecal contamination of recreational waters. Indicator bacteria are used to indicate recent faecal contamination (‘pollution’) as well as being used as indicators of health risk (by referencing
results to recognised guidelines). Indicator bacteria are clearly good indicators of recent
faecal contamination but imperfect indicators of health risk.

             The bacteria (generally faecal coliforms and/or enterococci) that indicate the presence of faecal contamination in waterways. Indicators are generally used to monitor recreational water quality, because searching for specific microorganisms that cause disease, such as viruses, is both difficult and costly.The number and variety of microbial agents that might be present in domestic wastewater is considerable.The routine monitoring for all the possibilities is either impossible or impractical. The time required to complete most of the analyses precludes their utility as a water quality control feedback tool.

             The solution to the problem has been the use of indicator bacteria that would be present when potential pathogen containing material (feces) was present. It should be emphasized that the presence of indicator bacteria does not mean the water contains pathogenic microorganisms but rather the potential exists for the presence of pathogens since the indicator bacteria point to the presence of fecal material in the sample. The number of pathogens that might be associated with the concentration of the indicator will be a function of the disease incidence in the community at the time the fecal material was disposed.

          The ideal indicator should:

1.) be present only when fecal contamination is present;

2.) exhibit the same or greater survival characteristics as the target pathogen for which it is a surrogate;

3.) not reproduce out side of the host; and,

4.) be readily monitored in a timely manner. At the present time no indicators in common use meet all these criteria.


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Guideline for Drinking Water Quality
(from GCDWQ, Health Canada 1996)

Parameter Maximum
Concentration a (mg/L)
Aesthetic Objective b (mg/L)
Coliforms (total or faecal) 0 c ­
Alkalinity Total ­ ­
Ammonia (NH4-N) ­ ­
Cadmium 0.005 ­
Calcium ­ ­
Chloride ­ <= 250 d
Chromium 0.05 ­
Copper ­ <= 1.0
Iron ­ <= 0.3
Lead 0.01(10mg/L) e ­
Magnesium ­ ­
Manganese ­ <= 0.05
Nitrate (NO3-N) 10.0 ­
pH ­ 6.5 to 8.5
Phosphorous ­ ­
Potassium ­ ­
Sodium ­f <= 200
Sulphate ­ <= 500
Temperature ­ <= 15oC
Total Dissolved Solids ­ <= 500
Total Hardness
(as CaCO3)
­ <= 200 g
Zinc ­ <= 5.0