Plugging the leaks


Malcolm Farley looks at the work of the IWA's Water Losses Task Force


The issues of water loss reduction, sustainability of source and supply, and cost-effectiveness of system operations have always been the bĂȘtes noire of water network operations. Over the last few years, however, water loss management has emerged as an integral task within network operation & maintenance (O&M) programmes, and has become a worldwide issue.

However, the gap between the sophisticated water loss and non-revenue water (NRW) reduction programmes in well-managed water utilities and the situation in many of the world's water utilities (especially in developing countries) is widening at a fast pace. Closing the gap has been the aim of the IWA Efficient Operations and Management Specialist Group, and, in particular, the work of its Water Losses Task Force (WLTF).
Their work has led to a set of performance indicators ideally suited to assess the water loss situation and to quantify the components of NRW. The last decade has seen the development of a comprehensive set of analytical tools, water loss reduction strategies and specialised equipment.

20 years ago, leakage assessment, monitoring and control was based more on a process of estimation than on precise science. This has changed dramatically, kick-started by the regulatory pressure on UK water companies to cut leakage.

Significant advances have been made in the understanding and modelling of water loss components, and on defining the economic level of leakage for individual systems. Yet, despite some encouraging success stories, most water supply systems worldwide continue to have high levels of water losses, many of which are almost certainly higher than their economic level.
Different strokes
Part of the problem has been the lack of a meaningful standard approach to benchmarking and reporting of leakage management performance. Surprisingly few countries have a national standard terminology and standard water balance calculation - and even then they all differ from one another. The IWA Specialist Group on Efficient Operations and Management, having worked for some years on performance indicators via its Performance Indicators Task Force1, identified water loss management as an issue for further study.

The specialist group hosted a leakage management conference in Cyprus, in November 2002, and the WLTF was formed at a meeting of some 70 of the delegates. The main topics and issues were identified by the members, teams were formed, and members joined a team of their choice and agreed to contribute to its work programme. The teams are:
  • Performance Indicators and Benchmarking,
  • Pressure Management,
  • Real Losses,
  • Apparent Losses,
  • District Metered Area (DMA) Manual,
  • Leak Detection Technology,
  • Publicity, Communication and Conferences.


  • As the reputation of the WLTF has spread, so have its numbers grown. It now consists of more than 100 water loss specialists worldwide - specialists from utilities, consultants and academia, all of them with a common interest in improving the way we approach water loss management, and in increasing our understanding of its components. The work of the WLTF to date has been summarised over the past two years in a series of articles in Water 21, the bi-monthly IWA journal, under the running theme of 'A Practical Approach'2.

    The WLTF has been a leader in developing and disseminating several new concepts. These include an international standard water balance with consistent terminology for real and apparent losses and the other components, strategies for water loss reduction, and corresponding performance measures. Many national standards have been developed using the IWA approach to water loss management, and it is clear from the international response that the strategies advocated by the IWA Task Force are garnering world-wide recognition as a best practice approach to reducing water loss. The standards have been adopted (with or without modifications) by national associations in a number of countries (for example Canada, Germany, Australia, New Zealand and South Africa), and, most recently, by the American Water Works Association (AWWA).
    A common language
    Drawing on the best practice from many countries, the IWA Task Force has produced an international best practice standard approach for water balance calculations (Figure 1), with definitions of all terms involved.

    The water balance calculation provides a guide to how much is lost as leakage from the network - real losses - and how much is due to apparent or "commercial" losses. Because of the wide diversity of formats and definitions used for water balance calculations internationally (often within the same country), there has been an urgent need for a common international terminology. Software packages are available to help the practitioner work through the water balance calculations.

    Using percentage unaccounted-for water (UFW) as an indicator has long been acknowledged as a misleading and inconsistent performance indicator. To address this the WLTF has developed a methodology for making international comparisons of water losses in a fair and consistent manner. The infrastructure
    leakage index (ILI) is a measure of how well a distribution network is managed; it takes into account a utility's operational practices as well as its performance in terms of the volume of losses. These parameters include pressure management, infrastructure condition, leakage activity and leak repair programmes. The ILI, which is the ratio of the current annual real losses (CARL) to the level of unavoidable annual real losses present in all systems (UARL), provides a much more accurate measure of utility performance than the traditional method of expressing water losses and non-revenue water as a
    percentage of water supplied.

    ILI = CARL / UARL

    The ILI can perhaps be best envisaged from Figure 2, which shows the four components of leakage management. The large square represents the current annual volume of real losses (CARL), which always tends to increase as the distribution network grows older. This increase, however, can be constrained by an appropriate combination of the four components of a successful leakage management policy. The white box represents the unavoidable annual real losses (UARL) - the lowest technically achievable volume of real losses at current operating pressure.

    On 5 May this year the UK members of the WLTF organised a seminar at the NEC in Birmingham, designed to disseminate its results and research findings to members of the UK water sector. The programme was designed to be of interest to a wide range of utility practitioners and consultants, who would benefit from learning about innovative approaches which they could apply to their own and to clients' networks.

    The seminar was sponsored by the Environment Agency, Hyder Consulting and Halcrow Water Services. Reflecting the applicability of the WLTF's work within the current regulatory framework, and the implications for leakage reporting methodology on future UK regulation, Rob Westcott, the EA's water resources policy manager (demand management), stated his belief that "the authoritative work of the WLTF should be disseminated more widely throughout the UK".

    The aim of the seminar was to motivate utility managers to establish a standard water balance, calculate the level of NRW, quantify its components and identify main problem areas. The seminar brought together the outputs from the WLTF - the new concepts and strategies for managing water losses based on programmes of data collection and research. The programme addressed some major issues for UK practitioners:
    n lessons to be learnt by the UK leakage industry from the application of IWA methodologies internationally,
    n comparing performance between utilities (the ILI performance
    indicator),
    n IWA leakage reporting methodology and the implications for future UK regulation.
    A marriage of two minds
    Two international guest speakers, WLTF Vice Chair Roland Liemberger and Alex Rizzo, shared their experiences of applying IWA strategies. Roland spoke on the challenges of applying the strategies in developing countries and Alex presented first-hand knowledge of using the methodologies in Malta WSC's network. Other speakers were WLTF UK members who have coordinated the work of the task force teams: Allan Lambert, John Morrison, David Pearson, Richard Pilcher, Stuart Trow, Steve Tooms and Malcolm Farley.
    Comments during the seminar and afterwards reflected the timeliness as well as the overall success of the event. In his presentation Stuart Trow said: "The practical approach to deriving an economic level of leakage which is being promoted by the WLTF is based on a technique we have called 'squeezing the box' (the CARL box in the Four Components diagram). Each component of water loss management follows a law of diminishing returns, and should be applied until its marginal cost reaches the value of the water in that supply zone."

    In his final presentation, Stuart wound up by asserting that "the purpose of the seminar was to let the UK know of the work of the WLTF and the ways in which we are applying new ideas to water losses management. Familiar faces from the UK have worked internationally since the Managing Leakage Reports were published
    ten years ago, and the many lessons learnt may help with understanding how the UK approaches water loss management in the future."

    Writing in the Demand Management Bulletin, Rob Wescott acknowledges the WLTF support for consultants and practitioners: "The WLTF has made available to leakage practitioners working abroad the practical tools missing for so long. The leakage performance indicators now allow consistent cross-company comparison to be made. The group's practical approach and wealth of experience must be acknowledged and this should encourage those responsible for managing leakage in England and Wales to think again."

    Liemberger was complimentary about UK practices, but less so of the performance indicators: "Although many of the concepts and ideas were not new to the audience, there was considerable interest in the holistic way the WLTF is applying and disseminating the 'package'. For obvious reasons interest from UK utilities was limited - they've been applying many of the concepts for years. But UK consulting engineers were very interested, especially in regard to working with international agencies such as the World Bank." Roland's message for the UK water industry was: "dispose of leakage per property or per km of mains and use international performance indicators (l/connection/day, average pressure and ILI) so everyone can understand your leakage situation".

    Allan Lambert agreed: "The presentation of international statistics on how management of pressures and surges reduces the frequency of new bursts, and burst repair costs, caused particular interest. This is because, although pressure management has been well established in the UK for many years, to date it has mainly been economically justified only in terms of its effect on flow rates of existing leaks".

    Allan provided a fitting conclusion by making some suggestions for how the IWA concepts can be progressed within UK utilities:
  • by showing additional justification for pressure management,
  • by encouraging the use of fixed and variable-area discharges (FAVAD) N13 as best practice standard approach for modelling pressure/leakage rate relationships,
  • by highlighting the continued use in Ofwat publications of leakage in m3/km mains/day, when the IWA work has shown that it is not an appropriate PI for UK systems, which have significantly higher connection densities/km of mains than most other countries,
  • by supporting EA initiatives to introduce the ILI as the most appropriate PI for annual leakage statistics for resource zones and companies,
  • by encouraging more UK utility personnel to participate in WLTF activities, notably Leakage 2005 in Halifax in September.


  • 1 Alegre H., Hirner W., Baptista J.M. and Parena R. (2000), Performance Indicators for Water Supply Services. IWA Manual of Best Practice. ISBN 900222272.
    2 http://www.iwapublishing.com/template.cfm?name=iwapwater21. Go to the home page for Water21 then choose preferred issue.
    3 Thornton J (2003) Managing Leakage by Managing Pressure - A Practical Approach. Water21 -
    Article No. 3. IWA Publishing.

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