Indicator organisms

Monitoring for specific bacterial pathogens is usually complex, expensive and time consuming. For these reasons, we verify your water quality by testing for a select group of organisms, known as indicator organisms.

Indicator organisms can be divided into two groups, those which are used as indicators of faecal contamination and those used as indicators of the efficacy of treatment and how safe the water is to drink.

1. Indicators of faecal contamination.

Most waterborne pathogens are introduced into drinking water supplies via contamination with human or animal faeces. These pathogens cause conditions ranging from mild to severe gastroenteritis, diarrhoea, dysentery, hepatitis and cholera.

Thermotolerant coliforms (bacteria) are always present in high numbers in human and animal faeces.

E.coli is the most common (typically >90%) and so is regarded as the most specific indication of recent faecal contamination in water.

While most thermotolerant coliforms are non pathogenic, there are some pathogenic subspecies of E. coli that can cause gastrointestinal illness.

E. coli (or thermotolerant coliforms ) should't be detected in a minimum 100mL sample of drinking water and so if detected, immediate action should be taken as it suggests a potentially serious water quality fault.

Treatment by chlorination or other acceptable forms of disinfection inactivates these microorganisms in water, provided the turbidity is low.

2. Indicators used in operational monitoring.

Coliforms are a diverse group of bacteria including Escherichia coli (E. coli) and other thermotolerant coliforms that are always present in the digestive tracts of animals and humans, as well as in plant and soil material.

As coliform bacteria occur widely in soil and water environments, there are many environmental coliforms that are not of faecal origin and so we no longer use total coliforms ( excluding E. coli )  as indicators for faecal contamination.

However, we do use total coliforms as indicator organisms for monitoring the efficiency of the water treatment and disinfection process as their presence may indicate inadequate treatment, breakdowns in system integrity (leaks, fractures or repair work) or the presence of biofilms.

Total coliforms are also used as a reasonable indication of the presence of pathogenic bacteria. Relatively easy to identify, coliforms are usually present in larger numbers than pathogenic bacteria and also respond to the environment, water and wastewater treatment similarly to many pathogens.

We offer a full suite of DNA tests for targeting input from microbiological and biological sources into water, from source water to treated water. These include:

Coliforms 1 /100mL

Thermotolerant coliforms - 1/100mL

E. coli - 1/100mL

Heterotrophic Plate Count – 1 /1mL

Sterile 600 mL PET bottle, Sodium thiosulphate dosed
Air gap essential
Transport and store at 4˚C
Process within 6 hrs of collection up to max 24hrs
(AS/NZS 2031)

We provide a range of NATA accredited analyses for Total Coliforms and E. coli. These include the rapid Defined Substrate Technology (Colilert), membrane filtration (MF) and most probable number (MPN), AS4276.

Colilert®18 is a commercially available Defined Substrate Technology which was designed for the simultaneous detection and confirmation of Total Coliforms and E. coli in water. The greatest advantage of this method is that it provides improved result turnaround times. Results are available within 18-22 hrs versus 1-4 days using traditional MF and MPN techniques.

We also provide NATA accredited analyses for Heterotrophic Plate Counts (AS4276) The count at 20-22oC will favour many environmental organisms, the count at 35-37oC will include both environmental and faecal organisms.