The New Good Practice Guide to Drinking Water Supply

The New Good Practice Guide to Drinking Water Supply Systems for the Management of Microbial Risk

The Good Practice Guide to the Operation of Drinking Water Supply Systems for the Management of Microbial Risk - Second Edition (the Guide, Figure 1), released in January 2020, is a Water Research Australia (WaterRA) member-funded initiative. The aim of the Guide is to provide managers and operational staff, who have the responsibility for the operation of drinking water supply systems, a concise reference document on the requirements for optimising the processes that are used to produce microbially-safe drinking water.

The second edition is a thorough rework of the original version, which was first published in October 2015. The Second Edition takes into consideration the many comments and reviews done by various organisations. Additional treatment unit processes have been included along with accompanying system evaluation templates.

IntroductionThe inclusion of the drinking water quality risk management framework into the Australian Drinking Water Guidelines (ADWG) in 2004 was a major step forward in the delivery of safe drinking water in Australia, but, by design, the ADWG is not a treatment handbook, but a policy document that details the risk framework, but not how risk management principles can be applied to specific treatment processes within a water treatment plant. In the absence of Australian-specific guidance, Australian water suppliers were using overseas documents, primarily from the US, and applying those to their treatment plants.

With the release of the Water Services Association of Australia’s (WSAA’s) Manual for the Application of Health-Based Targets For Drinking Water Safety (the WSAA Manual) in 2015 the need for Australian-specific guidance on how to practically implement microbial health-based targets (HBTs) within water treatment plants was highlighted.

To address this need, WaterRA and WSAA co-funded the production of the Good Practice Guide to the Operation of Drinking Water Supply Systems for the Management of Microbial Risk. The Guide was released in October 2015, as the companion document to the WSAA Manual, and it provided water suppliers with easy-to-follow advice on how to manage and optimise the most commonly-used water treatment processes for the management of microbial risk.

Since its release in 2015, the Guide has been well received, but, over time, it was recognised that it did not cover the full range of water treatment processes used in Australia, and some of the information in the Guide would be worth revisiting in the light of updated research and practice. In response, WaterRA initiated a process to update the Guide.

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/1Collaborate Innovate Impact

AuthorsKathy Northcott Water Research Australia

Mariela Wilson City Water Technology

Suzy McDonald GWM Water

Matthew Robertson Stephen Westgate TasWater

Ashley Sneddon Hunter Water

David Sheehan Coliban Water

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Good Practice Guide to the Operation of Drinking Water Supply Systems for the Management of Microbial RiskSecond Edition

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Final Report

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Figure 1: The new Good Practice Guide, now available to the water industry on the WaterRA website.

Networks and Treatments Updated June 16 2020

Catchment To Customer Risk ManagementThe catchment-to-customer risk-based approach to production of safe drinking water, is detailed in the Framework for Management of Drinking Water Quality (the Framework) found in the ADWG. This involves the identification and control of risks to drinking water quality, which is achieved through the implementation of a multiple barrier approach. This is where a number of different barriers (e.g. source protection, treatment) are put in place to prevent the risk of microbial contamination from the catchment reaching the customer. Whilst the risk management process stretches all the way from catchment to customer, in practice most risks are managed through the use of various water treatment processes.

Most Australian source waters require some level of treatment prior to being supplied to customers as drinking water. The level of treatment required to produce safe drinking water relates back to the overall quality of the source water and should be based on a system-specific risk assessment process, consistent with the approach described in the Framework set out in the ADWG.

Within this risk-based approach, the purpose of the Guide is to provide clear advice on appropriate preventive measures for the management of drinking water treatment processes and the distribution of treated water to consumers. This is achieved by providing targets, both numerical and observational, for the various activities that should be undertaken in order to produce microbially- safe drinking water.

The Basis Of The GuideThe Guide focuses on those processes typically found in conventional water treatment plants, including: chemical dosing for pH/ alkalinity adjustment; oxidation; powdered activated carbon dosing; coagulation; flocculation; clarification; media and membrane filtration; ozonation; granular activated carbon and/or biologically-activated carbon; disinfection using chlorine-based chemicals and/or UV irradiation; and wastewater management. It also covers general water treatment plant operation, raw water extraction and storage systems, raw water flow management, equipment and instrumentation, the distribution system and water quality information management. It does not consider the dosing of fluoride which is typically covered in detail by Codes of Practice in each state.

The Guide is based on the following key principles:

1. The ADWG Framework for Management of Drinking Water Quality (NHMRC and NRMMC, 2011), has been fully implemented and integrated into the operational practices of the water utility.

2. The water treatment plant is well designed, maintained and cleaned, such that the operation of the individual treatment processes is reliable.

3. Process monitoring is undertaken at appropriate intervals to inform operators of any changes to process parameters.

4. There is a competent and alert operations team, capable of responding rapidly to any changes within the water supply, treatment system or distribution system.

Interpretation & application

As mentioned in the previous section, the Guide is written based on the processes typically found in conventional drinking water treatment plants. It provides advice on the “required”, “supporting” and “desirable” measures that operations teams can check are in place, or implement, depending on the configuration of their plant. These recommendations are colour coded and are presented in a table that lists the measure, its rationale, recommended frequency of measurement and assessment and the desired or required result.

Entries in the Tables set out in the Guide are colour coded as follows (see Table 1 and Table 2).

Table 1: The colour coding and system of hierarchy for measures set out in the Guide.

Red A Required Measure that must be carried out to effectively manage the risks to the water supply

Amber A Supporting Measure for one or more of the Required Measures

Green A Desirable Measure



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A number of the Required Measures are requirements that will be established or carried out during the initial optimisation of a treatment plant, or even at the time a plant is designed and constructed. However, there are other Required Measures where regular assessment and reporting are required.

It is also important to note that water suppliers can clearly demonstrate the adoption of good practice in water supply optimisation by implementing the Required Measures.

Water supply system assessment

It is recommended that a water utility reviews their water supply systems against the Guide once every two years (biennially). The reason for recommending a two-yearly interval is that if the Guide is used as intended, the identification of deficiencies, but, more importantly, the actioning of the findings and the implementation of improvements, is likely to take more than 12 months for most utilities. It is further recommended to engage an independent expert approximately every 4 years to assess each drinking water system.

It is recognised that large water utilities have a greater capacity to more easily achieve all measures in the Guide; however, the measures have been designed to be achievable for all utilities.

Where the Guide is used by a utility and a number of gaps are identified, the suggested priority of improvement is in the order red then amber then green. Generally, the red measures have been listed in an approximate order of priority, so that the higher measures within each table should be implemented earlier than those later in the list.

Linking the Guide to other industry documents

The Guide is intended to form part of a suite of documents that provide advice on the production of microbially-safe drinking water, these documents being:

• The ADWG, which establishes the risk management framework for the production of safe drinking water.

• The WSAA Manual, which describes the steps to be taken to achieve safe drinking water based on the application of log reduction values (LRVs).

• The Guide, which provides advice on how to achieve the treatment objectives set out in the WSAA Manual.

The Guide can be used as a stand-alone document to assist in the optimisation of existing water supply systems, but it is preferable that it is used in conjunction with the ADWG and the WSAA Manual.



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Measure Rationale Assessment Interval Additional Information

2.2 Where alternative sources or alternative offtakes are available, the most suitable raw water source/offtake is used at all times.

The most appropriate raw water should be selected based on chemical parameters including DOC or UV254, the likely pathogen and cyanotoxin load, and the treatability of the water.

As Required

The monitoring interval should be based on the rate at which the raw water quality at a particular source can change.

Regular monitoring of alternative sources or alternative offtakes allows the most suitable raw water to be identified and used for treatment.

Jar testing will assist in determining the treatability of water from different sources.

2.3 Raw water extraction points and their immediate locale, including intake screens are regularly inspected for sources of contamination and findings recorded.

Inspection allows identification of contamination sources.

Quarterly

Intake screen cleaning should occur more frequently during periods of poor raw water quality.

Formal records confirm inspection and timely management of any potential sources of contamination.

2.4 Bore heads are fully sealed and the bore casings are regularly inspected and findings recorded.

Inspection allows identification of the potential for contamination.

Older casings should be inspected more frequently than new casings. 5 to 10 years is a suitable interval for casing inspections

Bore integrity should be included in the inspections and any flooding risk minimised.

Formal records confirm inspection and timely management of any potential sources of contamination.

2.5 Travel time of raw water from the source to the treatment plant is known for typical plant flows.

Knowing the actual time that a change in raw water quality will take to reach the treatment plant allows the operations team to accurately plan and prepare for the changes.

Biennially

And after any refurbishment or capital works.

Preparation of a flow vs travel timetable or relevant information included in an Operating Manual.

Table 2: An excerpt from the Guide, for Raw Water Extraction and Storage Systems, showing the Red-Amber-Green hierarchy for measures.


Good Practice Guide Case Studies

Case Study 1 – GWM Water

For Grampians Wimmera Mallee Water (GWMWater) the Guide provides a comprehensive framework for ensuring best practice in operations, and the safety of drinking water. GWMWater used the Guide in conjunction with other relevant documents to develop an internal audit program, ensuring compliance with Victoria’s Safe Drinking Water Act 2003 and Safe Drinking Water Regulations.

The internal audit program ran for three years (2017-18, 2018-19, 2019-2020) and included 19 water treatment plants and 12 booster chlorination stations. Of these, 14 treatment plants and 7 pump stations have been completed, with the remaining due for completion in 2020.

The main issues identified and rectified in the internal audit, relating to measures detailed in the Guide are shown in Table 3.

Table 3. Audit actions identified and rectified by the GWM Water team, relating to measures set out in the Guide

Issue categoryHow many audit items identified

and rectified

Reference in the first edition of the

GPG

Labelling 11 Pg. 11

Filter inspection 4 Pg. 21

Storage cleaning 3 Pg. 9

Calibration of instruments 1 Pg. 31

Servicing of monitoring equipment 1 Pg. 31

Jar testing 3 Pg. 15

CCP management 9 Pg. 37-38

GWMWater have also conducted other works triggered by a gap analysis of practices against the Guide including; a trial at a treatment plant where all three media filter backwash triggers (filter head loss, turbidity and time) were activated, collation of water age results through the distribution system, and an audit conducted of any potential interconnections between treated water and raw water reticulation within the distribution system. The backwash trial resulted in extending the run time from 30 hours to 110 hours, which had a flow on effect of helping the plant to run continuously where possible and resulted in water production gains and cost savings at the plant.

The First Edition of the Guide did not cover some other key technologies used in the water industry, such as GAC/BAC filters, PAC, and ozonation. The Second Edition of the Guide includes these key technologies, and updates the guidance to current knowledge to ensure best practice. The Guide will provide senior managers and operational staff, who have the responsibility for the operation of drinking water supply systems, a concise reference document on the requirements for optimising the processes that are used to produce microbially-safe drinking water.

Case study 2 – TasWater

TasWater had identified an issue where their compliance statistics (E. coli) were not providing an adequate representation of the water quality risks and issues operators faced in the field. In other words, some operators were not resourced or risk management plans were not renewed or managed on a suitably routine basis, to properly address water treatment plant (WTP) risks.

The impending microbial Health Based Targets (HBT) that are planned for incorporation into the ADWG will increase the levels of compliance required from a water authority. TasWater have aimed to get on the front foot and incorporate standards into new WTPs being developed and to retrofit older plants.



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Figure 2: Routine jar testing was identified as an area of improvement for the GWM Water team




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The review of the WTPs identified a large risk of water quality breaches, which were never found previously. This risk also places undue stress on operational staff already stretched in their day to day working environment.

To solve this problem, it was identified that a method of identifying and quantifying this risk was needed. This was achieved by making an assessment method tool, drawing on two key publications:

1. The “Manual for the Application of Health-Based Treatment Targets” (Water Services Association of Australia, 2015)

2. The “Good Practice Guide to the Operation of Drinking Water Supply Systems for the Management of Microbial Risk” (GPG) (Mosse & Murray, 2015).

The result is a visual representation of water quality risk on a chart. The closer to the bottom left hand corner of the chart a WTP is, the more risk and the greater chance of a water quality breach. The vertical axis represents the likelihood of risk (operational deficiencies) and the horizontal axis represents the impact of risk (the treatment deficiencies).

An example of how the tool can be utilised is where TasWater was able to demonstrate that with a combination of jar testing, sampling and instrument calibrations (vertical axis, Figure 3), together with optimisation

activities (horizontal axis, Figure 3) that includes filter and clarifier performance activities and the installation of UV treatment, a WTP would move from a very poor rating for risk of water quality issues to a much safer risk rating.

The solution takes critical and complex guides and methods, and presents it in a format that can be understood by TasWater Board members through to operators.

It has helped illustrate to the business where and what improvements need to be made. It has also helped fast-track much needed improvements. One practical result is the implementation and education around Operational Control Points (OCP) and Critical Control Points (CCP). This allows the operator to monitor specific quality standards in the treated water and provide control measures to prevent water being produced that is outside drinking water quality guideline values.

For the operator, the work has highlighted the importance of CCPs at WTPs, in particular filtered water turbidity, chlorine dosing and fluoridation levels in the final water. It also gives direction to the business where to put its capital investments in a targeted style according to maintaining compliant drinking water quality, potentially saving on holding back large capital outlays.

Figure 3: Assessed TasWater treatment plants using the visualisation tool, the object is to move plants from the red section in the bottom left up towards the top right of the graph.




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Case study 3 – Hunter Water

Hunter Water assessed their five water treatment plants against the Guide during 2018. The process was a valuable training exercise and also provided Hunter Water with a better understanding of microbial risk, in conjunction with previously undertaken Health Based Target Assessments. The improved understanding of microbial risk provided further weight in the justification of upgrades which may have been identified in the past but didn’t have a strong enough case to obtain funding approvals. Some of the areas for improvement which were identified and acted upon include; long sample lines, filter condition issues and spent backwash return deficiencies.

There were several examples of online meters being located a long distance from the sample point, leading to lags in monitoring and control of key water quality parameters. One case involved the pH measurement for coagulation control being located at the outlet of the floc tank in a direct filtration plant. During periods of stable water quality, this did not create issues. However, the water source is an on-river dam which experiences variable raw water quality during heavy rainfall, requiring rapid changes in coagulant dose and difficulty in controlling pH. While online instrumentation can trigger a plant shutdown to prevent treated water quality being compromised, there are associated operational and environmental risks faced in removing uncoagulated water from the plant in the event of a failure. The sample and meter

locations have recently been moved as a part of a broader upgrade of chemical systems at the plant. The reduced pH measurement lag, in conjunction with other chemical dosing improvements, have resulted in improved coagulation performance during wet weather events, although recent dry conditions have meant that there has not been a major wet weather event to fully test the new arrangement.

Another conventional WTP constructed in two stages during the 1970s had not had a detailed media filter inspection, involving excavation down to the nozzles, in over 10 years. This was identified during the assessment against the requirements set out in the Guide, and an inspection was undertaken in 2019. The inspection identified several issues, including foreign material in the filter media (roof sheeting, Figure 4), broken nozzles, high media sludge content and low media depth in some areas. While declining treated water quality has not been observed, an urgent refurbishment program for one of the filter trains is being developed.

Spent backwash recycle flows were critically reviewed across the three rapid gravity filtration plants. A deficiency was identified and remedied by a simple valve reconfiguration, resulting in spent backwash water being balanced evenly to both clarifiers. This avoided excessively high recycle rate through one clarifier in proportion to the raw water feed. Further instances of high recycle rates were identified which will require minor capital upgrades to rectify.

Figure 4: Filter inspections at Hunter Water showing foreign material found, using the requirements as set out in the Guide (courtesy Hunter H2O).



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Case Study 4 – Centroc

Centroc used the Guide to assess 13 of its drinking water supply systems from 9 member Councils. The assessments were undertaken by water treatment experts, with both operators and managers for each system present. The project also aimed to increase operator and manager knowledge to enable staff to self-assess and improve other plants in the future.

To assist with streamlined completion of the assessments, templates were developed that pre-populated summaries and graphs of the assessment outcomes. By doing this, the assessment was able to be completed efficiently and able to provide immediate feedback of the data collected on site.

Assessment of various supply systems enabled the identification of common areas of non-compliance across the constituent Councils. This enabled Centroc to develop common strategies to address and manage these shortcomings. Many of these improvements required little to no capital or additional operational cost. For example, very few systems assessed had any form of online monitoring at the raw water source. Given that many of the systems are interconnected and use the same source water, it was recommended that communication between Councils could be put in place as an initial step to allow for early warning of potential water quality events.

It was also apparent that many plants either didn’t regularly monitor or have the correct targets set up for settled water turbidity. By implementing the correct limits coupled with regular (preferably online) monitoring, plants were able to regain more control of their process and improve reliability in the treated water.

The outcome reports generated from the assessments provided Centroc and each constituent Council with a prioritised list of actions for each supply system to optimise their water treatment plants. This assessment was then able to be used as justification for the allocation of funds to complete these works.

ConclusionThe key outcome of this WaterRA member-funded initiative is the release of the Second Edition of the Good Practice Guide. This is aimed at encouraging managers and operational staff of drinking water utilities to adopt the measures in the Guide into their routine operations. The information contained in the Guide represents the best available knowledge on drinking water system optimisation for the Australian industry.

The hope is that when provided with plainly stated numerical and observational targets, managers and operators will adopt them, and this in turn will drive more consistency in the operation of WTPs and increase the assurance we have in the safety of the drinking water produced by our utilities.

AcknowledgmentsThe authors would like to acknowledge the work of Bruce Murray, City Water Technology and Peter Mosse, Hydrological P/L on both the first and second editions of the Guide, as well as the contribution of Richard Walker, Water Corporation of Western Australia and David Sheehan, Coliban Water Corporation.

Project Partners in the drafting of the First Edition (October 2015) included Melbourne Water, SA Water Corporation, Seqwater, Sydney Water Corporation, Sydney Catchment Authority and Water Corporation of Western Australia.

Project Partners in the drafting of the Second Edition (January 2020) included Coliban Water Corporation, Grampians Wimmera Mallee Water, Hunter Water Corporation, Urban Utilities, SA Water Corporation, Seqwater and Water Corporation of Western Australia.

ReferencesMosse, P, Murray, B (2015) Good Practice Guide to the Operation of

Drinking Water Supply Systems for the Management of Microbial Risk: Research Project 1074, Water Research Australia, Adelaide, South Australia.

NHMRC and NRMMC (2011) Australian Drinking Water Guidelines Paper 6 National Water Quality Management Strategy. National Health and Medical Research Council, National Resource Management Ministerial Council, Commonwealth of Australia, Canberra.

Water Industry Operators Association of Australia (2018) Problem Accepted Solution Supplied booklet – 2018. WIOA PASS awards booklet sponsored by Aqualift Project Delivery, Shepparton, Victoria.

Water Services Association of Australia (WSAA) (2014) Manual for the Application of Health-Based Treatment Targets.


Documents

The New Good Practice Guide to Drinking Water Supply