The following tables provide answers to common questions regarding Microbial health-based targets. This information can be found in Chapter 5 of the Australian Drinking Water Guidelines (the Guidelines):
|1||What are microbial health-based targets?||According to the World Health Organization health-based targets are: "measurable health, water quality, or performance objectives that are established based on a judgement of safety and on risk assessments of waterborne hazards". (WHO, 2010)
Microbial health-based targets provide a quantitative measure of the microbial safety of drinking water. The definition of microbial safety included in revisions to Chapter 5: Microbial Quality of Drinking Water is a health outcome target of 1x10-6 Disability Adjusted Life Year (DALY) (or 1 µDALY) per person per year (pppy). This is discussed further in Appendix 3: Derivation of microbial treatment targets for enteric pathogens.
|2||What is the purpose of introducing microbial health-based targets in the Australian Drinking Water Guidelines?||The Guidelines promote preventive risk-based management of drinking water quality from source to consumer with the Framework for Managing Drinking Water Quality (Chapter 3). Microbial health-based targets provide an assessment of pathogen risks in the water supply. Health-based targets also help inform appropriate measures (or 'barriers') for managing risk. These assessment and preventive measures support Elements 2 and 3 of the Framework.
Health-based targets are an operational benchmark rather than a pass/fail guideline value. Shortfalls in meeting treatment targets can be used to prioritise improvements. It is expected that full implementation of health-based targets into drinking water management will take time, particularly for small water suppliers.
For further information refer to section 5.4.3 Benchmark of Safety: Microbial Safety and the Water Safety Continuum.
|3||What are the major changes from previous versions?||This version includes numerous edits in response to the feedback provided during two rounds of consultation and to ensure content is based on recent publicly available literature. Also included in this current version is general guidance on implementation of health-based targets. The inclusion of implementation guidance with reference to relevant industry resources for practical information has been a consistent theme for all versions provided for consultation.|
|4||What is the evidence base for justifying the changes?||This version was developed with advice from the Water Quality Advisory Committee (the Committee) based on recent publicly available literature and best available published Australian data. The publications included in this update have been cited within the updated Chapter 5 and Appendix 3. Many of the changes made are in response to feedback obtained during public and industry consultation to improve guidance on implementation.
There is limited published data on concentrations of pathogens in Australian surface waters. NHMRC and the Committee have considered the best available information in the development of this advice. Water utilities may hold data, but this is not generally available for analysis by third parties. By publishing existing data, the accuracy of guidance on Quantitative Microbial Risk Assessment (QMRA) for drinking water in future revisions of the Guidelines could be improved.
|5||Where can I find the updated guidance?||The updated Guidelines are now published and available from the NHMRC website|
|6||Is there a timeline for adopting the updated guidance?||NHMRC has undertaken public consultation and consulted with stakeholders including the Water Services Association of Australia (WSAA) and the Environmental Health Standing Committee (enHealth) Water Quality Expert Reference Panel during the development of the advice to discuss any implications of adopting the new guidance.
It is expected that full implementation of microbial health-based targets into drinking water management, particularly for small water suppliers, will take time. Timelines for adoption in each jurisdiction will be dependent on the requirements set by the relevant health authority or drinking water regulator.
|7||Why has this update taken so long?||The guidance has been in development since 2009. It has been informed by multiple discussion papers, stakeholder workshops, and targeted and public consultations.
Following public consultation in 2016 on the initial draft guidance, NHMRC worked with representatives from the Committee and the enHealth Water Quality Expert Reference Panel to ensure all issues raised were given due consideration. This required extensive revision of the initial text to address stakeholder concerns. The revised guidance was released for public consultation in 2018. The extensive stakeholder feedback received was carefully considered by NHMRC and the Committee and edits made where accepted.
The final guidance was supported by the enHealth Water Quality Expert Reference Panel to include in the Guidelines. Details on the process undertaken to develop the guidance is outlined in the Administrative Report for this update, provided at Australian Drinking Water Guidelines.
|8||What are Log10 Reduction Values (LRVs) and LRV targets?||The target Log10 Reduction Values (LRVs) in Table 5.5 are the estimates of pathogen removal required for different source water categories to achieve the health outcome target of 1x10-6 DALY pppy.
The indicative pathogen LRVs potentially attributable to common treatment barriers are given in Table 5.6.
For simplicity a logarithmic scale is used to describe the values, as the pathogen reduction values can be anywhere in the order of thousands to millions.
|9||Why are the LRVs different from those used in other industry references?||NHMRC's approach to assigning LRVs is based on the best available recent Australian data and uses different assumptions to other commonly used industry references such as the 2015 WSAA Manual for the application of health-based targets for drinking water safety.
The final LRVs included in the revisions to the Guidelines were derived using recent publicly available literature and Australian data. While there are many high-quality industry documents available, these documents and the data within are not always available to the Committee or users of the Guidelines. Only publicly available scientific evidence that can be reviewed and endorsed are able to be used to inform NHMRC guidance.
NHMRC has been in consultation with WSAA during the development of the advice to discuss implications for water suppliers.
|10||How were the LRVs calculated?||An overview of the derivation of LRVs from first principles including assumptions are provided in Appendix 3: Derivation of microbial treatment targets for enteric pathogens.|
|11||Are LRVs given for other barriers such as large reservoirs?||The performance of pathogen removal in reservoirs is site-specific and should be evaluated for a range of conditions. General guidance for large reservoirs is provided in the revisions to Chapter 5 of the Guidelines.
Estimated LRVs for large reservoirs and catchments can be found in the Guidelines in Table A1.8 Estimated removals of enteric pathogens using multiple barriers.
|12||What site-specific validation is required to show the required LRVs are being achieved?||Providing detailed information on the process for site-specific validation of achieving required LRVs is out of scope of the revised guidance. Indicative values are provided in the revisions to the Guidelines in Table 5.6. However, these values do not represent validated LRVs for a particular treatment train.
Site-specific validation is critical to ensure that the treatment process is performing as expected (see section 9.8 Validation of barrier performance). Site-specific validation does not typically mean challenge testing and in many cases manufacturers of devices (for example, UV light disinfection systems and membrane filters) validate their devices before marketing them. In these cases, validation does not need to be repeated providing the operating conditions defined by the manufacturer are relevant to the site in question.
The basis for validating different processes is summarised in the revisions to Chapter 5 in Table 5.6, with reference to industry resources that provide more detailed guidance.
|13||The datasets used in the calculation of these LRVs do not represent tropical catchments – how can this provide nationally consistent guidance?||In the absence of published data on tropical catchments in Australia, the guidance is conservative so it can be applied nationally with reasonable confidence that it will be protective of public health. It is noted that there are limitations, but it is emphasised that discussions with the relevant health authority or drinking water regulator should be undertaken whenever there is doubt on site-specific applications.
NHMRC and the Committee have agreed that the evidence used in this revision of the Guidelines must be publicly available and peer reviewed. Guidance on tropical catchments can be developed as part of rolling revisions of the Guidelines should evidence become publicly available.
The guidance encourages discussions with the relevant health authority or drinking water regulator so that any exceptions are appropriately covered.
|14||For Category 1 sources why is there a 0 LRV target for viruses?||Fully protected Category 1 water sources are characterised as having negligible or no human access. An LRV target of zero for viruses is set as humans are the predominant source for enteric viruses.|
|15||What guidance is available on validating LRV credits for filtration based on filtrate turbidity?||Guidance on validated filter turbidity targets and LRV credits is provided in the Guidelines in Table 5.6. Further information on filtration and turbidity targets for pathogen removal can be found in the Turbidity Fact Sheet in Part V of the Guidelines.|
|16||Why is consumption of unheated (unboiled) drinking water assumed to be one litre per person per day?||Due to the sensitivity of enteric pathogens to heat, only the consumption of unheated water per person per day was considered in development of the guidance. The Australian Bureau of Statistics' Australian Health Survey (2012) reported the average amount of unheated (unboiled) water consumed by adult Australians as 1064 mL per day. This has been used to give a reference exposure volume (WHO 2016) of 1 L per person per day (which excludes heated water and other sources of drinks including soft drink, cordial and alcohol). Evidence from international review of drinking water consumption data reported an average consumption volume per person ranging from 718 to 964 mL per person per day citing Australian studies.|
|17||What influence does the average water consumption have on the calculation of LRVs?||Comparing the required LRVs using an indicative Cryptosporidium concentration of a Category 3 source water across both a 1 L and 2 L daily consumption of unheated water yields a result that differs by 0.3 LRV. With rounding, both calculated LRVs provide the same LRV. In some site-specific cases the outcome may differ from the example provided. Taking local circumstances into account should be discussed with the relevant health authority or drinking water regulator and calculated on a case-by-case basis when implementing the microbial health-based targets.|
|18||Why is an unsuitable source water vulnerability class not included in the revisions?||This is a considered decision of NHMRC based on the advice of the Committee. No source is out of question and some sources need to be considered given issues of water supply in some areas of Australia especially those areas experiencing drought.|
|19||Are drinking water sources other than surface water and groundwater covered?||The revisions to Chapter 5 of the Guidelines do not consider ocean catchments, roof water, storm water, greywater or sewage catchments. The general approach to monitoring and maintaining integrity of any water source is covered in the Guidelines in Chapter 3: Framework for the Management of Drinking Water Quality.|
|20||Why are there no specific classifications for groundwater sources?||Groundwater sources can become contaminated with enteric pathogens by a range of events. A high degree of caution needs to be exercised as multiple waterborne disease outbreaks have arisen where bores were incorrectly assumed to be secure.
Water treatment should be designed assuming that the risks in the groundwater are the same as those in the surrounding and recharging surface water, unless there is sufficient evidence of aquifer protection.
|21||How is the source water vulnerability classification validated?||The vulnerability classification process involves identifying sources of and barriers to enteric pathogen contamination within the water supply catchment(s) that provide water to the drinking water supply intake. A sanitary survey is an effective way to validate the assumptions of a vulnerability classification.|
|22||What validation is required when the comparison of the source water vulnerability and microbial indicator assessments are inconsistent?||The assessment results should be critically reviewed to understand the discrepancy. In the interim, the most conservative source water category under consideration should be adopted. These results should be discussed with the relevant health authority or drinking water regulator.
If the source water categorisation and required LRVs are considered by the water supplier to be unnecessarily conservative for a specific site, they must be discussed with the relevant health authority or drinking water regulator.
|23||What is the advice for the classification of drinking water sources where there is no or limited microbiological sampling data available?||In the absence of microbiological sampling data, the principle is to use a precautionary approach. Site-specific considerations and departure from the Guidelines should be discussed with the relevant health authority or drinking water regulator.|
|24||Why is the maximum or 95th percentile E. coli range the same for Category 2 and Category 3 source waters (Table 5.4)?||E. coli monitoring results alone are not enough for assigning a source water category, especially for discerning between Category 2 and Category 3 source waters. The vulnerability classification is an important step in differentiating between Category 2 and Category 3 source waters.|
|25||What information is required to complete a Quantitative Microbial Risk Assessment (QMRA)?||QMRA investigates the likelihood of disease along a risk pathway from the point at which pathogen concentration is quantified (for example, in a water source) to the receptor (for example, a consumer of drinking water). QMRA involves quantifying each component of the exposure pathway, together with the estimated health outcome. The outcome of a QMRA is a quantitative assessment of risk and is most applicable for answering quantitative questions such as: "What is safe?" and "How much treatment is required to achieve safety?"
Details on QMRA information and the assumptions applied to the LRVs in Chapter 5 are provided in Appendix 3. Figure A3.1 in Appendix 3 provides an overview of the QMRA framework and the information that is required. For additional guidance on information requirements for completing a QMRA refer to WHO (2016) Quantitative Microbial Risk Assessment for Water Safety Management.
|26||What should I do in the absence of real-world data for source water categorisation?||The source water category will need to be based on the vulnerability classification alone until sufficient raw water E. coli monitoring is undertaken. A conservative E. coli band allocation is recommended.
Site-specific issues should be discussed with the relevant health authority or drinking water regulator
|27||What happened to the previous tiered approach to site-specific assessment and QMRA?||The updated guidance focuses on site-specific assessment in consultation with the relevant health authority or drinking water regulator.
As new evidence becomes available, NHMRC and the Committee may consider including case studies on the site-specific use of QMRA as part of the rolling reviews to the Guidelines.
|28||Why is the process now more complicated with site-specific assessment included?||The updated guidance brings the Guidelines in line with current World Health Organization advice and other international guidance on managing the microbial safety of drinking water. The updates also provide nationally consistent advice on how microbial health-based targets are to be applied and assured.
While the process is more complicated when site-specific assessment is required, there is guidance on applying conservative default treatment targets in the absence of site-specific data. Discuss with the relevant health authority or drinking water regulator if there is any uncertainty or issues. While this approach may present a challenge for some water utilities, the process will enable a water utility to prioritise and plan improvements to its operation and work towards the goal of safer water and best practice.
The revisions to Chapter 5 aim to provide a useful general guide on how to achieve microbial safety of drinking water. Further practical or technical guidance can be found in the cited industry publications.
|29||This guidance does not go into the level of practical detail required by water utilities and relevant health authority or drinking water regulator – where can I get more technical information?||The revisions to Chapter 5 focus on the overarching scientific principles and concepts. A detailed guide for practical implementation is beyond the scope of the Guidelines. Further practical details can be found in industry implementation documents which are referred to throughout the text.
Useful references for further practical guidance can be found at the end of this document.
|30||Why refer to the relevant health authority or drinking water regulator for further guidance on site-specific issues?||The guidance has been prepared with the aim to provide general guidance on how to achieve microbial safety for drinking water. In some instances, there will be a need to resolve site-specific issues which fall outside the scope of the Guidelines. Engaging with a relevant health authority or drinking water regulator is recommended. This is because these agencies will have a high level of expertise and experience in dealing with a wide range of drinking water supply and public health matters within their jurisdiction.
The Guidelines are not mandatory standards and are recommendations only – it is up to the states and territories to implement them. The relevant health authority or drinking water regulator will be able to provide advice on local regulations and requirements.
|31||Useful references for further practical guidance||
Australian Bureau of Statistics, Australian Health Survey 2012. Australian Government, Canberra.
Water Services Association of Australia (WSAA) (2015). Manual for the application of health-based targets for drinking water safety. Water Services Association of Australia, ISBN 1 920760 68 7.
World Health Organization (WHO) (2010). Health-based targets, World Health Organization. Geneva, Switzerland.
World Health Organization (WHO) (2016). Quantitative Microbial Risk Assessment for Water Safety Management. World Health Organization. Geneva, Switzerland.