This protocol is derived from the Australian Drinking Water Guidelines
(the Guidelines) to guide Public Health Units (PHU) and water utilities in their joint response following rapidly changing source water quality, treatment failure, or microbial contamination.
Under Section 22 of the Public Health Act 2010, the Chief Health Officer has the power to issue advice, for the benefit of the public, concerning the safety of available drinking water and any possible risks to health involved in the consumption of that water. This may include a boil water alert. These powers are delegated to Public Health Unit Directors. A supplier of drinking water must issue to the public the advice provided under the Public Health Act, if so directed.
A regional water utility may issue a boil water alert of its own accord. However, before issuing a boil water alert, the water utility should liaise with their local PHU to discuss the situation.
Testing drinking water for specific pathogens is impractical and can be unreliable. For this reason tests are carried out for bacteria, which are present in faeces and indicate contamination. The Guidelines recommend monitoring microbiological quality by testing for Escherichia coli (E. coli). E. coli is the most reliable and specific indicator of recent faecal contamination in drinking water. The presence of E. coli in drinking water indicates recent faecal contamination because the organism generally does not multiply in drinking water systems.
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.
Thermotolerant (or faecal) coliform and total coliform bacteria are no longer recommended as primary indicators of faecal contamination. Although some members of these bacteria families are present in faeces, other members occur naturally in the environment 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.
NSW Health laboratory methods routinely provide total coliform as well as E. coli results. The Guidelines note that total coliforms are a poor indicator because they are normal inhabitants of soil and water, and can grow in water distribution 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. If detected, water utilities should check that disinfectant concentration is adequate, and that operation of the treatment plant and supply system is normal. Water utilities may set system specific targets for total coliform bacteria.
Further information on the microbiological quality of drinking water is available in the Guidelines (Chapters 5 and 10).
Action on the detection of E. coli or coliform bacteria
The water utility is responsible for carrying out all necessary investigation and resampling as specified in this response protocol.
- The water utility and the Public Health Unit (PHU) should be notified of the contamination by the testing laboratory (this must be immediate notification if E. coli is detected). Water utilities must record the chlorine concentration (free and total) and, if possible, pH and turbidity on the NSW Health sample label. Take a separate sample for these tests. Do not use the microbiology sample, as it will become contaminated.
- If total coliforms are detected (but not E. coli), the water utility should ensure adequate disinfectant concentration, check that the treatment plant and supply system are operating normally, and resume normal sampling. The next scheduled sample would normally be sufficient as follow-up. The water utility should consider system characteristics and analyse historical results when setting system specific targets for total coliforms.
- If E. coli is detected, the water utility should immediately investigate possible sources of contamination and increase disinfection (if inadequate). Check disinfection, treatment, source and supply system are operating normally, rectify any parameters that are not normal. Sources of contamination might include a treatment breakdown or malfunction (including failure to meet turbidity targets), a mains break, interruption to the supply, surges in water or power supply, or deliberate or accidental contamination of the system. The investigation may include an inspection of the system and associated service reservoirs by trained personnel. When found, the source of contamination should be rectified.
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.
- The water utility should resample at the same site using NSW Health Repeat Labels and record chlorine (free and total) and if possible pH and turbidity information. The sample should be submitted to a NSW Health Laboratory or other NATA accredited laboratory for analysis. Make sure that the laboratory knows that this is a repeat samples investigating possible contamination.
Note: If immediate resampling is not possible the water utility and Public Health Unit should assess the situation and agree on the necessary actions.
- If disinfection, treatment, source or supply system is not operating normally, consult PHU regarding boil water alert and rectification. The PHU should consider the need for a boil water alert if the water utility cannot provide timely confirmation of normal operation, including an adequate disinfection concentration.
- If E. coli is not detected in the repeat sample and no problem is found, resume normal sampling.
- If E. coli is detected in the repeat sample and/or a problem is identified through the investigation, consult PHU regarding boil water alert and rectification. Confirm adequate disinfectant concentration, resample at same site and other sites in the distribution system, conduct full sanitary survey and assess need for boil water alert (Section d).
- PHU Environmental Health Officers and Director should consult with the Water Unit and provide the findings of the water utility's investigation, when determining the need for a boil water alert. The NSW Office of Water should also be advised.
Action in response to a failure in treatment or disinfection, or poor or rapidly changing source water quality
- The water utility should immediately rectify the treatment or disinfection failure (i.e. failure to meet disinfectant or turbidity targets) and investigate possible cause of contamination. Additional operational or source water monitoring changes may be necessary.
- The water utility should assess source water changes:
If the treatment or disinfection failure cannot be corrected in a timely manner and there is not an adequate volume of treated water in storage, the water utility should contact the local PHU and collect an additional microbiology sample of the drinking water using NSW Health Repeat/Additional Labels and record chlorine (free and total) and if possible pH and turbidity information. The sample should be submitted to a NSW Health Laboratory or other NATA accredited laboratory for analysis. Make sure that the laboratory knows that this is a repeat samples investigating possible contamination.
- Determine if there is rapidly changing raw water turbidity that cannot be improved (e.g. by changing the level of offtake or source).
- Determine if there has been a recent inflow of water from a contaminated source in the catchment (even if raw water turbidity is not rapidly changing).
If the treatment or disinfection failure has been corrected and no E. coli is detected, resume normal sampling.
If the treatment or disinfection failure cannot be corrected and/or E. coli is detected in the repeat sample, consult the local PHU regarding boil water alert and rectification. Confirm adequate disinfectant concentration, resample at same site and other sites in the distribution system, conduct full sanitary survey, and assess need for boil water alert (Section d).
PHU Environmental Health Officers and Director should consult with the Water Unit and consider investigation/risk assessment outcomes in determining need for a boil water alert. NSW Office of Water should also be advised.
Corrective actions following the detection of contamination or treatment/disinfection failure
Corrective action may include one, or more, of the following:
- Increase disinfection at the treatment plant
- Correct treatment failure if possible
- Optimise treatment processes at the treatment plant
- Increase/add chlorine at points in the distribution system
- Clean, flush, and disinfect mains
Contamination investigation and sanitary survey - assessing the need for a boil water alert
The contamination investigation should aim to:
- Determine the origin of the contamination (e.g. is contamination present in water leaving the treatment plant or localised to one section of the distribution system?; is there evidence of pre- or post-treatment contamination?)
- Time and scale of contamination (i.e. the extent and likely recency of contamination)
The sanitary survey should consider whether barriers to contamination are adequate and whether treatment processes, including disinfection, are effective.
Barriers to the transmission of pathogenic microorganisms should include most, if not all, of the following:
- Selection of water sources which are protected from contamination by human and animal faecal material, and chemicals, and maintenance of an active catchment protection program
- Pre-treatment, such as detention and settling in reservoirs for sufficient time for pathogen die off
- Protection of water storages
- Extraction management
- Treatment (eg coagulation, settling, filtration)
- Disinfection of the water before it enters the distribution system
- Maintenance of adequate residual concentrations where chemical disinfection is used
- Security of the distribution system against re-contamination
Ensure the effectiveness of disinfectant concentration through particular attention to the following:
- Frequent (daily or continuous) monitoring of operational factors (e.g. pH, disinfectant residual, turbidity)
- No directly visible plant or animal material
- Minimum total chlorine residual of 0.5 mg/L after 30 min (if chlorination is used)
- Low turbidity, preferably <1 NTU
- pH optimised to suit the disinfectant used (subject to the need to minimise corrosion)
- Adequate maintenance of the reticulation system
- Frequent monitoring of disinfectant residual in the distribution system.
- If water temperature >30oC, monitor for amoebae
Factors to consider before issuing a boil water alert
The PHU, Water Unit and/or Chief Health Officer will consider the following when determining the need for a boil water alert or an alternative supply:
- are people exposed to an ongoing risk that could be prevented with a boil water alert?
- the findings of the contamination investigation and sanitary survey
- the effectiveness of current disinfection
- likelihood of identification and correction of the problem
- evidence of increased illness in present or previous events. The PHU should consider the need for enhanced surveillance
- estimate daily water consumption levels.
- determine if the samples are representative of water that is actually consumed?
- exposure duration and scale (how long and how many people been consuming the water?)
- have there been any complaints about water quality or health?
- are any vulnerable populations receiving the water? (i.e. dialysis patients, immunocompromised, etc.)
- will rectification measures affect any vulnerable populations? (i.e. disinfection changes and dialysis patients)
- whether proper sample collection and analysis techniques were used
- whether a NATA accredited laboratory analysed the samples
- availability of an alternative supply
- notification of consumers that may receive carted water from the affected system.
- the need to communicate accurate and appropriate information to the public in a timely manner
- the best means to communicate the information
- the community impact of any public health action.
Lifting a boil water alert
The PHU, Water Unit and/or Chief Health Officer will consider the factors listed in Section d as well as reviewing available test results. Where a water utility has issued a boil water alert it should consult the Public Health Unit about lifting the alert. The NSW Office of Water should also be advised.
See the flowchart
for a summary of the protocol described on this page.
The full protocol is also available for download: