Practical Guide to the Operation and Optimisation of Distribution Systems
P e t e r M o s s e a n d D a n D e e r e (S e c o n d E d i t i o n)
Second Edition, June 2009
Foreword to the First Edition The provision of water services to communities in developed countries has been the single most important development in improving public health at the population level. It has been much more significant than any other factor, notwithstanding the improvements in medical science over the past 100 years. It is also true that lapses in the operation and maintenance of water and waste water treatment facilities and the associated distribution networks have resulted in illness and deaths in affluent societies. If one looks at significant water quality incidents that occur in developed countries, the problems are usually due to the lack of adequate professionalism on the part of management, regulators and/or operational staff, rather than any basic inadequacy of the infrastructure involved. People in affluent societies do not expect to die or be made ill from using public water supply systems and this is quite a reasonable expectation. Water quality management is a vital and important role. People with primary responsibilities for water quality management, whether at the “coal face” or at a senior or executive level should appreciate the importance of this function. Complacency, inattention and distraction from the core tasks are dangerous features in water utilities. One often hears comments like “I would like to pay more attention to filter backwashing operations but I just don’t have the time”. Unless one wants to be a central player in a water incident, then we need to ensure that the right priorities are applied. Water quality guidelines have developed significantly over the past few decades in Australia and elsewhere. The emphasis in the past has been on compliance with tables of numbers that defined the quality of water that had to be produced for distribution - ultimately to the customer’s tap. In the early days, compliance was more or less optional for many of the water authorities, due to the powerful positions the utilities often held in the government bureaucracy. The strengthening of regulatory systems and the use of operating licenses and stronger legislation has improved matters substantially in this regard. The Australian Drinking Water Guidelines (ADWG) now includes a Water Quality Management Framework that sets out a risk based process of proactively managing water quality from its source through to the customer tap. It involves a thorough understanding of each system and the active management of a number of interventions that ensure that the outcome will always be optimal and safe. Compliance should be automatic. It is a logical and straightforward process, but, in some areas of the system, there can be a lot involved in sorting out the detail. It is with this area of detail in mind that the authors of this series have decided to produce this excellent set of practical guides that will assist operators with responsibilities for key control points in water operations (eg filtration, distribution). The national water quality guidelines, (ADWG in Australia), regulatory changes, licenses and audits all tend to confront water utilities from the top down. These guides are intended to be helpful at the operational “coal face”. Collectively, all of these relatively recent additions to the water quality management landscape should help to ensure that there are no adverse public health outcomes from the use of public water supplies in Australia. I commend the authors of this series for their excellent initiative and I trust that the series will be helpful in ensuring that we get the very best level of performance and reliability out of our water treatment facilities. Professor Don Bursill CEO, Cooperative Research Centre for Water Quality and Treatment (1995-2005) Chair of the Coordinating Committee for Review of the ADWG (1996-2004)
Acknowledgements
The authors wish to thank Greg Ryan of South East Water for critical review of the manuscript and for assisting in preparation of the section on corrosion. Thanks are also extended to Vince Sweet of SA Water and Dharma Dharmabalan of Central Highlands Water for assisting in preparation of the section on the management of chloramination in distribution systems. Thanks also to Jill Busch of Gippsland Water for the chlorine demand test method. The authors also wish to acknowledge the contribution of all the sponsors who have provided funding for the publication of this book. Particular thanks are due to the Water Industry Operators Association (WIOA) for their commitment to improving the skills of operations staff in the water industry and for coordinating the development of this resource as part of the process. The efforts of WIOA CEO, George Wall, in proof reading the final document and for organising the layout and publication of this book have been invaluable. Thanks to Aqualift P/L for Figures 4.1 to 4.9 Thanks to Nordical Diving Services for Figures 4.10 to 4.17 PREFACE TO THE SECOND EDITION In preparing the second edition we have included new material that relates to the impact of the distribution system on public health. A number of studies have become available since publication of the first edition that clearly show that management or perhaps mismanagement of the distribution system can have an impact on public health. The old saying that no one has become ill is no longer acceptable. These studies prove it isn’t so. We have also included more photographs and small amounts of new information throughout other parts of the guide. Peter Mosse and Dan Deere May 2009.
General Introduction This series of Practical Guides to Water Treatment focuses on each of the major steps in the process from catchment to tap, namely 1. Catchment 2. Coagulation and clarification 3. Filtration 4. Distribution 5. Disinfection Each guide provides practical advice regarding the management and operation of each of the critical control points identified by utilities as they implement the Australian Drinking Water Guidelines Framework for the Management of Drinking Water Quality (ADWG 2004), the Safe Drinking Water Act 2003 in Victoria, or a HACCP program. An underlying objective of each of the guides is that on each and every page operational staff should be able to make mental notes to themselves along the lines of • That’s a good idea • We should be doing that • We can start on that immediately The guides are not about identifying costly solutions but simply identifying ways to get the best out of what is available at any particular time. The aim is to provide suggestions and hints that can be implemented easily, cheaply and immediately in the field. Finally, the Australian Drinking Water Guidelines are concerned “both with safety from a health point of view and with aesthetic quality of drinking water”. These guides deal with both of these aspects; not just with safety aspects. They are about getting the absolute best out of the system, so as to deliver the absolute best quality drinking water to the consumer. Chapter 2 is common to all of the guides and provides a general background to the concepts of hazards, risks and control points developed in the Australian Drinking Water Guidelines.
Feedback Requested These guides have been written to help operators perform their jobs effectively and to help operators understand the vitally important roles they fulfil within the water industry. The authors would be pleased to receive any feedback on this guide. Suggestions for further information or areas where additional explanation would have aided understanding can all help to make any future editions stronger and more useful for operators in our industry. Any suggestions can be directed by e-mail to the Water Industry Operators Association (WIOA) at info@wioa.org.au or by post to 22 Wyndham Street, Shepparton, Victoria, 3630.
Contents Foreword Acknowledgements General Introduction Chapter 1 Distribution Systems And Public Health...........................................................7 Chapter 2
Chapter 3
Chapter 4
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Hazards, Risks and Control Points
Hazards and Drinking Water......................................................................................... 11 Pathogens are the Main Hazards in Drinking Water...................................................... 11 Other Hazards...............................................................................................................14 Control Points................................................................................................................14 Critical Limits and Target Criteria..................................................................................16 Monitoring.....................................................................................................................16 Responsibilities.............................................................................................................17
Distribution System Targets
The Importance of Good Distribution System Operation...............................................18 Operating Criteria and Performance Parameter............................................................18
Distribution System Optimisation
• 1. Know Your System....................................................................................................24 Valves..............................................................................................................24 Mains...............................................................................................................25 Disused System Components..........................................................................25 • 2. Prevent Contamination..............................................................................................26 In Treated Water Storages...............................................................................26 In Distribution Mains.........................................................................................30 Maintain positive pressure at all times..............................................................30 Keep Mains in Good Repair and Above the Levels of Ground Water...............31 Avoid rapid increases in flow............................................................................31 Avoid Water Hammer.......................................................................................32 Install Backflow Prevention Devices.................................................................32 Use Sanitary Maintenance Procedures............................................................33 • 3. Ensure Minimum Detention Times............................................................................33 In Treated Water Storages...............................................................................33 In Distribution Mains.........................................................................................34 • 4. Optimise Disinfection................................................................................................35 • 5. Maintain Disinfectant Residuals................................................................................36 • 6. Balance Chlorine Residuals Across The System.......................................................38 • 7. Install Residual Trim Chlorination..............................................................................40 • 8. Use Materials Compatible With Drinking Water.........................................................41 • 9. Stabilise Water Entering The Distribution System.....................................................41 • 10. Minimise Copper Corrosion.....................................................................................42 • 11. Optimise Chloraminated Distribution Systems.........................................................45 Nitrification.......................................................................................................46 Monitors And Management Of Chloramated Systems......................................46
Chapter 5
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Chapter 6
Chapter 7
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Monitoring Distribution Systems
Essential Monitoring Equipment....................................................................................48 More Sophisticated Monitoring Equipment....................................................................49 Monitoring Disinfection..................................................................................................50 Laboratory Testing.........................................................................................................52 E coli................................................................................................................53 Total Coliforms.................................................................................................53 Heterotrophic Plate Counts..............................................................................54 Integrated Analysis........................................................................................................54 Consumers As Water Quality Monitors..........................................................................55 Pattern Analysis............................................................................................................55 Proactive Taste And Odour Surveys..............................................................................56
Maintaining A Clean Distribution System
Flushing........................................................................................................................59 Air Scouring...................................................................................................................59 Swabbing......................................................................................................................60 Which Cleaning Method Is Best?..................................................................................61 How Much Does Cleaning Cost?...................................................................................62 How Often Should The System Be Cleaned?................................................................62 Mains Cleaning, Drought And Wasted Water................................................................64 Keeping Treated Water Storages Clean........................................................................65
Mains Breaks, Mains Replacement And New Mains
Sanitary Operating Procedures.....................................................................................67 New And Replacement Mains.......................................................................................67 Swabbing.........................................................................................................68 Hydrostatic Pressure Testing............................................................................68 Disinfection.......................................................................................................69 Testing..............................................................................................................69 Mains Breaks................................................................................................................69 Disinfecting Mains What To Do With The Discharged Water.......................................................................73 Approved Materials.......................................................................................................74 Work Teams And Management Practices......................................................................74
Chapter 8
Operational Verification Audits.........................................................................76
Chapter 9
Closing Words. .......................................................................................................78