This protocol is derived from the Australian Drinking Water Guidelines (the Guidelines) to be used by Public Health Units (PHU) and water utilities to guide their joint response following the detection of physical and chemical water characteristics that exceed the Guidelines.
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 recommendation for the provision of an alternative supply of water or a “do not drink” advice. 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.
The Australian Drinking Water Guidelines have set aesthetic and health related guideline values for physical and chemical characteristics. Aesthetic guideline values are set at the concentration that ensures water is aesthetically pleasing in terms of taste and odour, and can be used without causing corrosion of plumbing or staining. Health-related guideline values are set at the concentration that, based on current knowledge, does not result in any significant risk to the health of the consumer over a lifetime of consumption.
Further information on the physical and chemical quality of drinking water is available in the Guidelines (Chapters 6 and 10). Where both aesthetic and health-related guideline values are exceeded, consider health related characteristics first and then aesthetic characteristics.
Action on the exceedance of guideline values
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.
- The water utility and the PHU should determine if a potential acute health risk exists. Consider the type of guideline value (health-related or aesthetic) exceeded, the concentration, and potential causes such as a major contamination event or treatment failure. Further information is available in the fact sheets for physical and chemical water quality in the Guidelines.
- If a potential acute health risk exists, the water utility should consult with the PHU and the NSW Office of Water (NOW) regional inspector regarding immediate action such as rectification, alternative supply, public warnings, and investigation and sampling. The PHU should contact the Water Unit.
- If no acute health risk is present the water utility should conduct an investigation, in consultation with the local PHU and the NOW regional inspector, to determine the possible sources of contamination. These might include a treatment breakdown or malfunction (e.g. chemical overdose), a mains break, corrosion, interruption to the supply, surges in supply, or deliberate or accidental contamination of the system. The investigation may include a visual inspection of the system and associated service reservoirs by trained personnel. When found, the source of contamination should be rectified.
- The water utility should resample at the same site upon advice from the PHU using NSW Health Repeat Labels, unless specific project labels are issued. The sample should be submitted to a NSW Health Laboratory or a NATA accredited laboratory for analysis. Make sure that the laboratory knows that this is a repeat samples investigating possible contamination.
- If the repeat sample meets the guideline value resume normal sampling.
- If the repeat sample exceeds the guideline value use available data to assess risk (see Risk assessment).
- If the risk assessment does not indicate an ongoing risk, resume normal sampling.
- If the risk assessment indicates an ongoing risk, the water utility should consult with the PHU and the NOW regional inspector regarding rectification (e.g. flushing, system maintenance, etc.), alternative supply, public warnings, and investigation and sampling. PHU Environmental Health Officers and Director should contact the Water Unit.
Risk assessment and considerations for public notification
The Water Utility, PHU, and NOW regional inspector should consider the following when conducting the risk assessment:
- Routine sampling frequency.
- Water utilities that collect two routine chemistry samples per year for the affected supply system should discuss, with the PHU, the need for a sampling investigation either through a project or change in the routine sampling frequency.
- Statistical analysis of available data or sampling investigation results.
- For health-related guideline exceedances, calculate the 95th percentile of results over (at least) the last twelve months.
- For aesthetic guideline exceedances, calculate the mean of results over (at least) the last twelve months.
- Estimate daily water consumption levels.
- Determine if the samples are representative of water that is actually consumed?
- Exposure duration (how long have people been consuming the water?
- Have there been any complaints about water quality or health?
- Are flow-on effects possible? Such as low pH causing lead and copper contamination through corrosion of plumbing.
- Are any vulnerable populations receiving the water? (i.e. dialysis patients, immunocompromised, infants, etc.)
Further information on conducting health risk assessments is available in Section 3.2.3 of the Australian Drinking Water Guidelines and via enHealth's list of environmental health publications.
Public notification considerations
The PHU, Water Unit and/or Chief Health Officer will consider the following when determining the need for public notification, a do not drink advice, or an alternative supply:
- The outcomes of the risk assessment.
- 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.
Also see the flowchart from the NSW Drinking Water Monitoring Program booklet.