Testing drinking water for specific pathogens is impractical and can be unreliable. It is neither physically nor economically feasible to test for all pathogens that may be present in drinking water. For this reason tests are carried out for bacteria, which are present in faeces and indicate contamination of drinking water. The Australian Drinking Water Guidelines (the Guidelines)recommend that Escherichia coli (E. coli) is the most reliable and specific indicator of recent faecal contamination in drinking water. Refer to the E. coli factsheet in the Australian Drinking Water Guidelines for further information.
Additionally, the turnaround time for microbiology test results is typically at least 24 hours after sample collection and may be delayed for remote utilities. By the time a test result is available, the tested water has already entered the distribution system and been consumed.
Thermotolerant (or faecal) coliform and total coliform bacteria are no longer recommended by the Guidelines as primary indicators of faecal contamination. Although some members of these bacteria families are present in faeces, other members occur naturally in soil and water in the absence of faecal contamination. Coliform bacteria other than E. coli can multiply in treated drinking water under the right conditions. Even E. coli can multiply in raw water under some conditions but generally not in drinking water systems.
Total coliforms should generally not be detected in water sampled immediately after disinfection. While total coliforms are not a reliable indicator of faecal contamination, their presence may suggest regrowth or possible ingress of foreign material. In some cases, E. coli may lodge in biofilm and be released at a later time. Flushing and resampling may be necessary to confirm whether contamination is persistent.
Testing for E. coli can help verify the adequacy of preventive measures. However, water utilities should not rely solely on end point testing. The implementation of a comprehensive risk-based drinking water management plan is the most reliable way to protect drinking water quality.
This page forms part of the NSW Health response protocol for water utilities and public health units: Managing pathogen risks in drinking water
Contact your local Public Health Unit on 1300 066 055 and refer to: