Evolution of the Turbidity Fact Sheet in the ADWG and its link to the management of Cryptosporidium risk

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1 Evolution of the Turbidity Fact Sheet in the ADWG and its link to the management of Cryptosporidium risk David Sheehan Member, NHMRC s Water Quality Advisory Committee

2 Turbidity Turbidity the basics Measuring turbidity gives an indication of the particulate matter in drinking water Is typically measured by measuring the amount of scattering that occurs when you pass a beam of light through water The unit of measurement is Nepholometric Turbidity Units (NTU)

3 Uses of turbidity for assessing drinking water quality Turbidity can be used in three ways in relation to assessing drinking water quality: Aesthetics customers relate the turbidity of the drinking water they receive to its safety; low turbidity water avoids aesthetic issues Disinfection turbid water can compromise the effectiveness of chlorine and UV disinfection Filtration the turbidity of water post-filtration can be used as surrogate measure for the effectiveness of the filtration process

4 Turbidity ADWG 1996 version of the ADWG was the first version to be released under the National Water Quality Management Strategy (NWQMS) Introduced Fact Sheets for key water quality parameters

5 Turbidity ADWG Guideline Value from Turbidity Fact Sheet Based on aesthetic considerations, the turbidity should not exceed 5 NTU If disinfection is required, then a turbidity of less than 1 NTU is desirable at the time of disinfection

6 Turbidity ADWG Chapter 5 System Management

7 Turbidity ADWG 2004 ADWG introduced the Framework for Management of Drinking Water Quality (risk management framework) Greatly expanded the number of Fact Sheets for key water quality parameters Added in Information Sheets for key water quality concepts

8 Turbidity ADWG Information sheets on disinfection were included, that noted that the desired turbidity at time of disinfection was <1 NTU Guideline value statement unchanged: Based on aesthetic considerations, the turbidity should not exceed 5 NTU. If disinfection is required, then a turbidity of less than 1 NTU is desirable at the time of disinfection.

9 2004 to 2011 ADWG 1996 and 2004 guideline value statements often misinterpreted Was considered that the turbidity of the water leaving the water treatment plant could be up to 5 NTU, regardless of the treatment processes being used, as this was the turbidity value that applied at a customer s tap This was considered a situation that had to be rectified in the 2011 ADWG, as this interpretation was potentially leading to poor treatment performance, and the possible production of unsafe drinking water

10 Turbidity ADWG For the 2011 ADWG, the Turbidity Fact Sheet was redrafted to recognise the role that turbidity has as a: Measure of filtration performance Determinant of the efficacy of disinfection Aesthetic characteristic Guideline value was broken into these three distinct sections

11 Turbidity ADWG GUIDELINE for - Chlorine-resistant pathogen reduction: Where filtration alone is used as the water treatment process to address identified risks from Cryptosporidium and Giardia, it is essential that filtration is optimised and consequently the target for the turbidity of water leaving individual filters should be less than 0.2 NTU, and should not exceed 0.5 NTU at any time Where filtration alone is used includes the circumstance where there is a clarifier upstream of the filters ( alone refers to use of a single barrier that is designed to remove chlorineresistant pathogens)

12 Turbidity ADWG GUIDELINE for - Chlorine-resistant pathogen reduction: Guideline value does not make it a requirement to install filtration Where filtration is used to manage pathogen risk the filtration process must actually control the risk (i.e. the process must actually work) Xagoraraki et al. (2004) demonstrated that to achieve effective removal of Cryptosporidium and Giardia a post-filter turbidity of < 0.2 NTU was required

13 Turbidity ADWG GUIDELINE for - Chlorine-resistant pathogen reduction: USEPA and NZ-MOH based their standards on < 0.15 NTU The approach that should be taken is that the further below 0.2 NTU the filter operates, the more effective the removal of Cryptosporidium and Giardia will be If a filter is operating above 0.5 NTU, it is not operating as an effective barrier to chlorine-resistant pathogens

14 Turbidity ADWG GUIDELINE for - Chlorine-resistant pathogen reduction: It is recognised that some filters were originally installed to manage aesthetic issues, and were not designed to operate below 0.2 NTU If a subsequent risk assessment has shown that chlorine-resistant pathogens are a hazard that needs to be managed, then either: The filter needs to be upgraded to operate at below 0.2 NTU An additional barrier to manage chlorine-resistant pathogens needs to be installed (e.g. UV irradiation)

15 Turbidity ADWG GUIDELINE for - Disinfection: A turbidity of less than 1 NTU is desirable at the time of disinfection with chlorine, unless a higher value can be validated in a specific context. Disinfection guideline value recognises that the effectiveness of chlorine disinfection decreases with increasing turbidity Guideline value not suggesting that turbidity can rise between filtration and chlorination, but where chlorination is used alone, the desired turbidity at time of disinfection is < 1 NTU

16 Turbidity ADWG GUIDELINE for - Disinfection: Guideline recognises that effective disinfection can occur at turbidities above 1 NTU (e.g. most of Melbourne s water supply) If chlorination (or any other disinfection process) is going to occur [routinely] above 1 NTU, then the effectiveness of the disinfection process needs to be validated/verified

17 Turbidity ADWG GUIDELINE for - Aesthetics: Based on aesthetic considerations, the turbidity should not exceed 5 NTU at the consumer s tap. This guideline value recognises that during distribution drinking water may gain turbidity from within the distribution system In most cases, this is an aesthetic issue, not a health issue This guideline value should not be interpreted as meaning that the treatment target is 5 NTU, and every effort should made to minimise the turbidity of water supplied to customers

18 Cryptosporidium ADWG Guideline value statement (i): No guideline value is set for Cryptosporidium due to the lack of a routine method to identify human infectious strains in drinking water. If such a guideline were established, it would be well below 1 organism per litre and would involve testing of impractically large volumes of water.

19 Cryptosporidium ADWG Guideline value statement (ii): A multiple barrier approach from catchment to tap is recommended to minimise the risk of Cryptosporidium contamination. Protection of catchments from human and animal wastes is a priority. Operation of barriers should be monitored to ensure effectiveness.

20 Cryptosporidium ADWG Guideline value statement (iii): Although routine monitoring for Cryptosporidium is not recommended, investigative testing may be required in response to events that could increase the risk of contamination (e.g., heavy rainfall, increased turbidity, treatment failure). If Cryptosporidium is detected in drinking water, the relevant health authority should be notified immediately. All necessary measures to assess and minimise public health risks should be implemented as soon as possible.

21 Cryptosporidium ADWG Take home messages: Direct monitoring for Cryptosporidium is unlikely to be the best way to manage the associated risk Preferable to: control likely sources of Cryptosporidium in catchment area Ensure treatment barriers are operating effectively

22 Coliban Water s region of operation 19 water treatment plants 49 towns supplied with drinking water Approximately 145,000 customers serviced Area of operation covers almost 10% of Victoria

23 Relative size of water supply systems Number of supplies per category Population served per water supply system < >20000 Population served

24 Goornong WTP Filtration Unit Goornong WTP services ~300 customers

25 Coliban Water Coliban Water is in the process of implementing WSAA s HBT Manual Whilst most filtration systems can get close to meeting the <0.2 NTU requirement, some require optimisation In some cases, additional barriers are likely to be necessary (e.g. UV systems) Aim is to achieve required log reduction values to reduce risk to the equivalent of 1µDALY

26 Coliban Water Yearly average turbidity at contact point (NTU) Average Turbidity at entry point (Nov 14 to Oct 15)

27 Questions