Concepts

BACKGROUND AND BURSTS ESTIMATES (BABE) (1993)
This internationally applicable overview concept was developed by Allan Lambert for the UK National Leakage Control Initiative, for calculating components of Real Losses based on the various parameters which influence them.

In BABE analyses, components of Real Losses on different parts of the infrastructure (service reservoirs, mains, service connections etc )are considered to consist of:

BABE analyses can be used for calculating components of Annual Real Losses, or components of night flows. For annual Real losses calculations, by assuming that average run-times of detectable leaks and bursts consist of three time elements – Awareness, Location and Repair time – Utility policies and standards of service can be modelled. Typical burst flow rates are specified at a standard pressure, and are adjusted to actual pressure using appropriate assumptions for FAVAD N1 values (see next item).

FIXED AND VARIABLE AREA DISCHARGES (FAVAD) (1994)
Pressure: Leak Flow Rate Relationships
Japanese and UK research data on pressure:leakage rate relationships have been reconciled with other test data worldwide using the FAVAD concept, first proposed by John May. The velocity of flow of a leak varies with the square root of pressure and a Coefficient of Discharge (Cd); but FAVAD also recognises that the effective area of some leakage paths – Cd x A – may vary with pressure. The simplest versions of the FAVAD equation are

Leakage Rate L (Volume/unit time) varies with Pressure N1  or  L₁/L₀ = (P₁/P₀)^N1

N1 values can be calculated from tests on Sectors at night; values derived for sectors in the UK, Japan, Brazil, Cyprus, USA, Australia and New Zealand have shown that  N1 generally varies between 0.50 and 1.50, with occasional values up to 2.5. Small undetectable leaks at joints and fittings (background leakage) typically have N1 values around 1.50, as do larger leaks and bursts on flexible pipes. Detectable leaks and bursts on rigid pipes normally have N1 values close to 0.50.

The PressCalcs software explains the FAVAD concept and includes a quick method for assessing the N1 exponent based on the Infrastructure Leakage Index (ILI) and the % of rigid pipes in the system. The N1Test worksheet explains the theory of an N1 night step test..

The FAVAD concept is used in the CheckCalcs, PressCalcs and SRELLCalcs softwares for modelling relationships between pressure and leak flow rates, and pressure and components of residential consumption.

UNAVOIDABLE ANNUAL REAL LOSSES (UARL) (1999)
The first IWA Water Loss Task Force (1996-99), chaired by Allan Lambert, developed a system-specific equation for the lowest technically achievable Real Losses, for well managed infrastructure in good condition. Substituting appropriate parameter values in a simplified ‘BABE’ component analysis of annual Real Losses, an equation was derived which allows the Unavoidable Annual Real Losses (UARL) to be calculated for most systems (subject to some lower limits on size of system and average pressure).

UARL is a useful concept as it can be used to predict, with reasonable reliability, the lowest technically annual real losses for any combination of mains length, number of connections, customer meter location and average operating pressure – assuming that the system is in good condition with high standards for management of Real Losses.  UARL is also used in the calculation of the Infrastructure Leakage Index (ILI).

There is also a different equation for calculating Unavoidable Background Leakage in volume/hour, for component analysis of night flows. A ten-year review of the international application of UARL and ILI (Lambert, 2009) can be downloaded from the Technical Papers Section of this Website.

IWA BEST PRACTICE STANDARD WATER BALANCE (1999/2000)
Drawing on the best practice from many countries, the first IWA Water Loss Task Force, and the IWA Performance Indicators Task Force, produced a standard approach for Water Balance calculations with definitions of all terms involved, which was published in 2000.

This was a major step forward, and the IWA Water Balance is now used and recommended in an increasing number of countries, by technical organisations, regulators, and international funding agencies. The use of confidence limits in Water Balance calculations, included in the PIFastCalcs software, provides valuable insights into the reliability of the calculated Real Losses volume, and the priorities for action for improving the reliability of the calculations.

IWA BEST PRACTICE PERFORMANCE INDICATORS (1999/2000)
The first IWA Water Loss Task Force identified the best traditional simple performance indicators for Non-Revenue Water and operational management of Real Losses, and also improved performance indicators for these parameters (%NRW by value, and Infrastructure Leakage Index). These were initially published in several papers and reports between 1999 and 2000. Since then, many hundreds of ILI values have been calculated and compared, from many different countries.

METRIC benchmarking is used to compare performance indicators from different Utilities with different key characteristics (mains length, number of service connections, customer meter location, average pressure). The ILI was specifically developed for this purpose by the 1st Water Loss Task Force, and is now widely recognised as the best international performance indicator for metric benchmarking of Real Losses management.

For PROCESS benchmarking - measuring progress towards targets for Real Losses in an individual Utility - the ILI is not the most appropriate performance indicator, if pressure management is part of the Real Loss reduction strategy. Instead it is recommended to use:

4 COMPONENTS APPROACH TO MANAGING REAL LOSSES (1999)
The first version of this widely used diagram was developed by David Pearson, and it has since been further enhanced to include economic leakage levels. It is now widely used internationally as a simple means of explaining the basic activities that are required for effective operational management of  Real Losses . 

TWIN TRACK APPROACH TO MANAGING REAL LOSSES (2002)
This first appeared in a paper by Lambert & McKenzie at the IWA Conference ‘Leakage Management – A Practical Approach’ in Cyprus in November 2002. It emphasises that

• the Infrastructure Leakage Index (ILI) measures how well real losses are being managed at the current pressure
• but the current pressure regime is not necessarily optimal, and there are often pressure management options that will have additional and substantial benefits in terms of reductions in leak flow rates, new burst frequencies, repair costs and other benefits

ECONOMIC INTERVENTION      (2005)
Calculation of economic intervention frequencies in the UK, based on continuous night flow measurements in small zones, had been in use since 1994. However, outside the UK, many Utilities did little or no active leakage control, and a simpler method was needed. Lambert & Fantozzi (July 2005) and Lambert & Lalonde (September 2005) proposed a simpler method of calculating economic intervention frequency based on regular survey, using only 3 key parameters:

• Variable cost of Real Losses (CV)
• Cost of an Intervention (CI)
• Rate of Rise of Unreported leakage

Using this practical approach, Utilities can quickly calculate annual budget requirements for an economic frequency of intervention in any size of system, together with the consequent annual average volume of unreported leakage. See the paper by Lambert & Lalonde in the Technical Papers Section of this website for more details.

This approach also greatly simplifies the assessment of Short-Term Economic Leakage Levels. The Economic Intervention methodology forms an integral part of the ALCCalcs and SRELLCalcs softwares.

PRESSURE:BURST FREQUENCY RELATIONSHIPS (2005)
Collection of burst frequency data ‘before’ and ‘after’ pressure management in over 100 individual zones by IWA Task Force members has clearly demonstrated that remarkable reductions in new burst frequencies can be achieved in some cases, by quite moderate reductions in maximum pressure (including reduction of surges). Allan Lambert leads the research in the Pressure Management Group of the IWA Water Loss Task Force on how best to model and predict this effect. The latest prediction methods are included in thePressCalcs and SRELLCalcs softwares. See paper by Thornton & Lambert (2007) in the Technical Papers Section.

ECONOMIC LEAKAGE LEVELS, WITH AND WITHOUT PRESSURE MANAGEMENT (2008) The development of quick and practical methods for calculating economic leakage levels has been an objective of the Water Loss Task Force since 2001. Methods developed in the United Kingdom in the 1990's were data intensive and did not consider the influence of pressure management on leak flow rates, burst frequency and repair costs, and frequency and costs of economic intervention. Confidence Limits also needed to be included for meaningful calculations.

In 2008, using the concepts developed for Economic Intervention and Pressure:Burst Frequency relationships, ILMSS Ltd developed the most advanced international software for calculating Short Run ELL (SRELLCalcs), with or without pressure management, with confidence levels. SRELLCalcs is currently being applied to Utilities in North America. See paper by Fanner & Lambert (2009) in Technical Papers Section.