Infrastructure Leakage Index (ILI) as Water Losses Indicator

Abstract

The key in developing a strategy for management of non-revenue water (NRW) is to gain a better understanding of the reasons for NRW and the factors which influence its components. The components of NRW can be determined by conducting a water balance analysis. The International Water Association (IWA) provides a water balance calculation that gives guidance to estimate how much is lost as leakage from the network (physical losses), and how much is due to non physical losses. Further, IWA has established the Infrastructure Leakage Index (ILI), a performance indicator for comparisons of leakage management in water supply systems. This paper introduces ILI and reasons why it is a more appropriate approach to use than the percentage of system input volume.

Full text

6
Civil Engineering Dimension, Vol. 11, No. 2, September 2009, 126-134
ISSN 1410-9530 print / ISSN 1979-570X online
Technical Note:
Infrastructure Leakage Index (ILI) as Water Losses Indicator
Winarni, W.
1
Note from the Editor
The key in developing a strategy for management of non-revenue water (NRW) is to gain a
better understanding of the reasons for NRW and the factors which influence its components.
The components of NRW can be determined by conducting a water balance analysis. The
International Water Association (IWA) provides a water balance calculation that gives guidance
to estimate how much is lost as leakage from the network (physical losses), and how much is due
to non physical losses. Further, IWA has established the Infrastructure Leakage Index (ILI), a
performance indicator for comparisons of leakage management in water supply systems. This
paper introduces ILI and reasons why it is a more appropriate approach to use than the
percentage of system input volume.
Introduction
The annual volume of water losses is an important
indicator in assessing water utility efficiency, both in
individual years and as a trend over a period of
years. High and increasing water losses are an
indicator of ineffective planning and construction,
and also of low operational maintenance activities.
In developing countries, the combination of water
losses with poor sanitation and intermittent supplies
often gives impact to a serious health risk.
Key to establish a strategy for management water
losses is to gain a better understanding of the
reasons for losses and the factors which influence its
components. Significant advances have been made
by some water utilities in the understanding and
modeling of water loss components, and in defining
the economic level of leakage. Yet, despite some
encouraging success stories, most water supply
systems worldwide continue to have high levels of
water losses.
Some countries have established water balance
analysis, but unfortunately a wide diversity of
formats and definitions are used, often within the
same country.
1
Email: winarni@trisakti.ac.id
Environmental Engineering Department, Trisakti University,
Jakarta, Indonesia
Note: Discussion is expected before November, 1st 2009, and will
be published in the “Civil Engineering Dimension” volume 12,
number 1, March 2010.
Received 31 October 2008; revised 19 January 2009; accepted 8
March 2009.
Part of the problem has been the lack of a
meaningful standard and performance indicator (PI)
in reporting, benchmarking and comparing the
actual water losses management performance
between different utilities. Being aware of the
problems of the wide diversity water balance formats
and methods, practitioners have identified an urgent
requirement for a common international terminology.
Drawing on the best practice from many countries,
International Water Association (IWA) Task Forces
on Water Losses and Performance Indicators have
produced an international best practice approach for
water balance calculation. [1]
Furthermore, in the recent years, IWA Task Forces
have developed and tested the usage of
Infrastructure Leakage Index (ILI) as a water losses
performance indicator. ILI accommodates the fact
that real losses will always exists, even in the very
best and well managed distribution system. The
international PI can give the most rational technical
basis for comparisons water losses between utilities,
which can be used by the operators to measure their
attempt in water losses reduction.
International Water Balance
Any discussion relating to water losses must be
preceded by a clear definition of water balance
components. The level of water losses can be
determined by conducting a Water Audit (North
American term) with the result shown in a Water
Balance (international term). To be consistent with
international terminology, the term of water balance
is used in this paper.
126

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
127
Water balance is based on measurements or
estimations of (i) water produced, (ii) water imported
and exported, (iii) water consumed, and (iv) water
lost. The water balance calculation provides a guide
to estimate how much is lost as leakage from the
network (‘real’ losses), and how much is due to non-
physical losses (‘apparent’ losses). This calculation
allows the practitioner to answer the question of
‘how much water is being lost?’
The water balance is computed over a 12 month
period, thus represented the annual average of all
components. The components of water balance
should always be calculated as volume before any
attempts is made to calculate performance
indicators. Considering the problem of different
water balance format and methods, the IWA has
developed an international standard of water
balance structure and terminology as shown in
Figure 1 [1]. Meanwhile, this standard format has
been adopted by national associations in a number of
countries and also by American Water Works
Association (AWWA). [2].
Definitions of principal components of the IWA
water balance are as follows:
- System Input Volume is the annual volume input
to the particular part of the water supply system.
- Authorised Consumption is the annual volume of
metered and/or non metered water taken by
registered customers, the water supplier and
others who are implicitly or explicitly authorized
to do so. It includes water exported, leaks and
overflows after the point of customer metering.
- Non-Revenue Water (NRW) is the difference
between System Input Volume and Billed
Authorised Consumption. NRW consists of:
• Unbilled Authorised Consumption (usually a
minor component of the water balance).
• Water Losses.
- Water Losses is the difference between System
Input Volume and Authorised Consumption,
consists of Apparent Losses and Real Losses.
- Apparent Losses consists of unauthorised
consumption due to all type of metering
inaccuracies.
- Real Losses are the annual volumes lost through
all types of leaks, bursts and overflows on mains,
service reservoirs and service connections, up to
the point of customer metering.
Nowadays, the term of ‘water loss’ and ‘NRW’ are
internationally accepted, and have replaced the term
of ‘unaccounted-for water’ (UFW) since there is a
wide interpretation of the term UFW and less
consistent which make inter-country comparison
more difficult. Besides, the water balance shows that
all losses can be accounted for. Therefore the IWA
Task Forces do not recommend using of this term
anymore.
Water Losses and Leakage
Non-Revenue Water
Non-revenue water is a volume of water which
enters the distribution system but does not give any
revenue to the utility, loss of revenue. NRW includes
not only the real losses and apparent losses, but also
the unbilled authorized consumption.
Unbilled authorized consumption is normally only a
small component of the water balance. Its includes
items such as fire fighting, flushing of mains and
Billed Metered Consumption
Billed Unmetered Consumption
Unbilled Metered Consumption
Unbilled Unmetered Consumption
System Input Volume Unauthorized Consumption
Metering Inaccuracies
Water Losses
Leakage on Transmission and/or
Distrubution Mains
Real Losses
Leakage and Overflows at
Utility's Storage Tanks
Leakage on Service Connections
up to point of Customer Metering
Billed Authorized
consumption
Revenue water
Authorized
Consumption
Non Revenue Water
(NRW)
Unbilled Authorized
Consumption
Apparent Losses
Figure 1. International Standard Water Balance and Terminology – IWA [1].

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
128
sewers, cleaning of distribution storage tanks, filling
of water tankers, public hydrants, street cleaning,
watering of municipal gardens, public fountains,
frost protection, etc. They may be metered or
unmetered, according to local practice.
The available documentations of such usages often
show that the volumes of unbilled authorised
consumption are unnecessarily high. It can be
managed down to lower annual volumes without
influencing operation efficiency of customer service
standards. For this reason, such volumes should be
metered wherever feasible.
Water Losses
Besides definition as mentioned above, water losses
can also be defined as a difference between NRW
and unbilled authorized consumption. It is important
to differentiate between water loss and leakage,
since not all losses are the result of leaking pipe and
poor infrastructure. As can be seen in Figure 1,
water loss is apparent losses (non-physical losses and
management losses) and real losses (physical losses).
Leakage is usually the major component of water
loss in developed countries. But this is not always
the case in developing countries, where illegal
connections, meter error or accounting errors are
often more significant. Water theft and illegal
connection are often the result of local customs,
combined with tariff structures or inadequate
metering policies.
As the magnitude of the two components of water
losses, real and apparent losses, is known, it is
possible to:
- Predict the potential savings (from real losses)
and potential revenue increases (from apparent
losses).
- Develop real and apparent losses reduction
strategy.
- Set realistic targets.
Not all countries have the luxury or well developed
network infrastructure. Many are struggling to
ensure that their customers receive a reasonable
water supply to sustain health and life, often in a
network with outdated infrastructure, poor record
systems, inadequate technical skills and technology,
an unsuitable tariff structure or revenue collection
policy, and a poor operation and maintenance policy.
Programme to reduce apparent losses will usually
dependent on longer term of changes to metering,
regulatory and legislative policies.
Factors Influencing Real Losses
There are several local factors which constrain
performance in managing real losses. Based on a
reference data set of 27 diverse water distribution
systems in 20 countries used by Lambert et al [3], it
was found that these factors can vary widely
between individual distribution systems, i.e.: (i)
length of mains, (ii) number of service connections,
(iii) location of customer meters on service
connections, (iv) average operating pressure, and (v)
continuity of supply.
The real losses in the water balance are the leakage
occurs in the distribution system up to the metering
point. Therefore the ’number of service connections’
is logically preferable to the ‘number of properties’,
since there is a possibility that a single service
connection serves a much larger properties.
However, even where apartments are individually
metered, the water balance calculation is usually
based on the leakage up to a single master meter on
the service connection. [1, 4].
In many systems, the customer meter is located close
to the street/property’s boundary and the service
pipe between the main and the customer meter is
owned and maintained by the water utility. In case
the customer meter is located some distance after
the street/property’s boundary, the leakage on the
private pipe between the street/property’s boundary
and the customer meter should be included in the
real losses component. It should be considered since
the practitioner experiences that, in most well run
systems, the largest volume of real losses is
associated with service connections rather than
main.
Many countries recognize pressure control as a
technique for managing leakage, but there are local
limits to the lowest acceptable average pressures
that can be achieved. The average frequency with
which new leaks occur, and rates of flow of
individual leaks, is very sensitive to operating
pressures. The observed weighted average
relationship for large systems appears to be that
leakage rates vary with pressure to the power of
1.15. The simplified formula is that leakage rate
vary linearly with operating pressure except at very
high of very low pressure.
The percentage of time for which the distribution
system is pressurized is an important parameter to
be included in real losses estimation. This can be
achieved by expressing the annual volume of real
losses as a volume per day ‘when the system is
pressurized’ (w.s.p.). The average operating pressure
should also be calculated over the period when
system is pressurized.
Besides the local factors mentioned above, the type of
soil/ground can influence the frequencies of leaks

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
129
and burst, and the speed with which leaks and
bursts become visible at ground surface. These real
losses can be undetected for a long period. However,
correct selection and laying of pipe materials and
modern leakage control methods can reduce these
influences significantly.
Performance Indicators for Management
of Real Losses
Performance indicators provided in the Manual of
Best Practice of IWA [1] which are used to compare
the performance of water losses management are:
- Water losses and real losses as a % of system
input volume.
- Water losses per house connection.
- Water losses per km of mains per day (density of
connections < 20 per km of mains).
- Infrastructure Leakage Index (ILI).
Percentage of System Input Volume
Water losses as a percentage of system input, which
is a traditional indicator, is easily calculated and is
certainly the most common indicator quoted by non
specialists, including politicians and the media. They
incorrectly believe that this is the most meaningful
measure of performance for NRW, Undoubtly it is
better than have no target at all. But this indicator is
unsuitable for assessing the efficiency of management
of distribution system, since the values of percentage
NRW are:
- Strongly influenced by consumption (and changes
in consumption).
- Influenced by the high pressure (above average
pressure).
- Difficult to interpret for intermittent supply
situations.
- Not distinguishable between apparent and real
losses.
For many years, technical groups in Germany and
the United Kingdom draw attention to the undue
influence of consumption and changes in
consumption, when water losses are expressed as a
of system input volume. The same volume of real
losses can have a different percentage of losses
depending to the consumption. If average real losses
are 100 litres/service connection/day, then real losses
as percentage of system input would be (i) 29% for
consumption of 250 litres/connection/day, or (ii) 1%
for consumption of 8000 litres/connection/day.
When consumption decreases, seasonally or
annually, or due to demand management measures,
the percentage of real losses increases even if the
volume of real losses remains unchanged. When
consumption increases, the opposite effect occurs.
This influence of consumption is demonstrated in
Figure 2 whereas the curved line represents the
same real losses of 200 liters/connection/day. [5].
Figure 2. Influence of Consumption on Water Losses as percentage of System Input Volume [5].

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
130
There are also problems of interpreting percentage of
real losses in the situation of intermittent supply. A
system with 12 hours supply per day may easily has
only 20% real losses. But what would this figure look
like in the uninterrupted supply situation? Consider
that all burst will leak for 24 hours instead of 12 and
thus twice as much water would be lost. This
problem is found in Southeast Asia since
intermittent supply is quite a common occurrence as
reported by Asian Development Bank, 1997 [6]. It
mentioned that Seoul (South Korea) has 34% losses
with 24 hours supply per day, but Karachi
(Pakistan) has 30% losses with 1 – 4 hours supply
per day. Also Chennai (India) with 4 hours supply
has losses of 20%. Seoul is certainly not worse than
Karachi and Chennai.
Water Losses per House Connection
Considering that water losses as percentage of
system input volume only shows water resources
efficiency for the top management, and does not
provide any information on management of
distribution system, IWA recommended operational
PI per service connection (m³/connection/year).
Experience from practitioners shows that the
frequency of leaks and bursts, and of the annual
volume of real losses, are several times higher on
service connections rather than mains since there
are large number of joints and fittings on service
connections between the main and the edge of the
street. Although average burst flow rates are higher
for mains than for service connections, when typical
proportions of unreported bursts, and average
durations of different types of bursts, are taken into
account, it is evident that in most systems the
largest volume of annual real losses generally occurs
on service connections. [5].
There will of course be some systems where the
greatest proportion of real losses will be associated
with the length of mains, rather than the service
connections. In well managed systems, this ‘break-
point’ occurs when the density of connections is
around 20 per km of mains [1, 4]. Therefore, for the
density of connections less than 20 per km of mains,
IWA provides indicator as water losses per length of
mains (m³/km length of mains/year).
In the case of systems subject to intermittent supply,
this indicator expressed as ‘litres/service connection/
day when the system is pressurised’. The annual
volume of real losses is divided by the equivalent
number of days that the system is pressurized,
rather than by 365 days. This indicator allows for
comparison between distribution systems with
variations in supply time.
The Infrastructure Leakage Index, ILI
Even though using traditional indicator ‘volume/
service connection/day when system is pressurised’
allow comparisons between systems with different
level of supply, however this indicator still does not
take operating pressure into account, which is a
major disadvantage. Also, it is influenced by
difference of connection density and distance of
customer meter to street/boundary.
In 1997 Allan Lambert (in Liemberger [6]) realized
the need for a real losses performance indicator
which would allow international comparisons
between systems with very different characteristics,
e.g. intermittent supply situations, low and high
pressure systems, differences in consumption levels
and so on. Therefore IWA recommended the use of
ILI, abbreviation of Infrastructure Leakage Index,
which is categorized as level-3 indicator i.e.
indicators that provide the greatest amount of
specific detail but are still relevant at the top
management level [1].
The ILI, which in the first few years known to only a
few insiders, is now widely accepted and used by
practitioners around the world, as it best describes
the efficiency of the real loss management of water
utilities. It is a measurement of how well a
distribution network is managed (maintained,
repaired, and rehabilitated) for the control of real
losses, at the current operating pressure. [3, 6]
ILI is the ratio of Current Annual Real Losses
(CARL) to Unavoidable Annual Real Losses (UARL),
or ILI = CARL / UARL. Being a ratio, the ILI has no
units and thus facilitates comparisons between
countries that use different measurement units
(metric, U.S., British).
Concept of Infrastructure Leakage Index
This section describes the concept of ILI, to get better
understanding how water balance and ILI could
identify the priorities to address in leakage
management strategy.
Real Losses Management Strategy
ILI can be better explained using Figure 3, which
shows primary components of leakage management.
The area of the large rectangle represents the
Current Annual Real Losses (CARL) for any specific
system. As the system ages, there is a tendency for
natural increasing rate of real losses through new
leaks and burst, some of which will not be reported
to the utility. This tendency is controlled and
managed by some combination of the four primary
components, namely (i) pipeline and assets
management, (ii) pressure management (which may
increase or decrease the pressure), (iii) speed and
quality of repairs, and (iv) active leakage control to
locate unreported leaks.

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
131
The number of new leaks arising each year is
influenced primarily by long-term pipeline
management. Replacing an old main with a new
installation will undoubtedly reduce leakage from
the main. However, unless the service connections
are also renewed, the benefit may not be as great as
first estimated. Reducing the time it takes to repair a
leak will also reduce the volume of leakage. The
average duration of the leaks is limited by the speed
and quality of repairs, and the active leakage control
strategy controls how long unreported leaks run
before they are located.
Real losses can be severe, and may go undetected for
months or even years. The volume lost will depend
on the characteristics of the pipe network and the
leak detection and repair policy practiced by the
utility, i.e. [7]:
- The pressure in the network.
- The frequency and typical flow rates of new leaks
and bursts.
- The proportions of new leaks which are ‘reported’.
- The ‘awareness’ time (how quickly the loss is
noticed).
- The ‘location’ time (how quickly each new leaks is
located).
- The repair time (how quickly it is repaired or
shut off).
- The level of ‘background’ leakage (undetectable
small leakage).
Pressure management is one of the fundamental
elements of a well-organized leakage management
strategy. The effective schemes are those which
cover a large area and which make a significant
impact on average pressures.
The benefits of pressure management are:
- Extension of the life of the distribution
infrastructure.
- Reduction of new burst frequencies on
distribution mains and service connections.
- Reduction of flow rates of all leaks and bursts
present in the system at any time.
- Reduction of new leaks on private pipes and
overflows at private storage tanks.
- Reduction of some components of consumption
subject to direct mains pressure.
Unavoidable Annual Real Losses, UARL
Leakage management practitioners are well aware
that real losses will always exist, even in the very
best systems. The volume of Unavoidable Annual
Real Losses (UARL) which is the lowest technically
achievable annual real losses for a well maintained
and well managed system, is represented in Figure 3
by the smaller inner rectangle. The difference
between CARL (large rectangle) and UARL (small
rectangle) is the potentially recoverable real losses.
UARL is a useful concept as it can be used to predict,
with reasonable reliability, the lowest technical
annual real losses for any combination of mains
length, number of connections, customer meter
location at current operating pressures, assuming
that the system is in good condition with high
standards for management of real losses and there
are no financial or economic constraints.
It is just a question of how high these UARL will be.
IWA Task Forces have developed a ‘user friendly’
pressure-dependent formula for predicting UARL
values in a wide range of distribution systems [3],
i.e.:
UARL (litres/day) = (18 x Lm + 0.8 x Nc + 25 x Lp)
x P (1)
Potentially Recoverable
Real Losses
UARL
Pressure
Management
Speed and
Quality of Repairs
Active Leakage
Control
CARL
Figure 3. Basic Methods of Managing Real Losses. [5]

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
132
Where Lm is mains length in km, Nc is number of
service connections, Lp is the total length of
underground pipe between the edge of the street and
customer meters in km, and P is average operating
pressure in meter.
This formula considers real losses for modeling and
calculation purposes:
- Background losses from undetectable leaks (i.e.
at joints and fittings), which flow rates too low for
sonic detection if non-visible. Typically low flow
rates and long durations.
- Losses from reported leaks and bursts, based
from experiences of frequency, typical flow rate,
average duration target. Typically high flow rates
but short duration.
- Losses from unreported leaks and bursts, based
from experiences of frequency, typical flow rate,
average duration target. Typically moderate flow
rates but durations depend on the method and
intensity of active leakage control.
- Pressure, whereas the correlation between
pressure and leakage rate assumes to be linear.
With current knowledge and experience, UARL can
be calculated for any system with more than 5000
service connections, density of connections greater
than 20 per km mains, and operating pressure
between 25 – 100 metres. [3, 4]
Application of ILI
The ratio of the CARL to the UARL (ILI) is a
measure of how well the three infrastructure
management functions – repairs, pipelines and asset
management, active leakage control – are being
undertaken separates from the aspects of pressure
management.
In the beginning of developing the ILI methodology,
based on international utilities data collected by IWA
Water Losses Task Forces [5], North West England
Utilities [8], North America and Australia [4], it
found the maximum value of ILI is 14. It is
important to note that this ILI is a result from the
systems which had reasonable data and active policy
to manage real losses. Since 1999, many more ILI
values have been calculated for systems in more
than 40 countries which show utilities with ILI in
excess of 100.
Although a well managed system can have an ILI of
1.0 (CARL = UARL), this does not necessarily have
to be the target as the ILI is a purely technical
performance indicator and does not take economic
considerations into account. For any water
distribution system there is a level of leakage below
which is it not cost effective to make further
investment or use additional resources to drive
leakage down further. In other words, the value of
Infrastructure Leakage Index (ILI)
Connection Density (numbers / km)
Figure 4. Relationship of ILI to Connection Density in North West England. [8]

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
133
the water saved is less than the cost of making
further reduction.
The variation of ILI shows a positive relationship
with connection density, the higher the density the
higher the ILI, as explain in Figure 4. Pearson [7]
had identified that it was likely to be a result of:
- The longer location times in more complex urban
areas.
- The longer reparation times due to road access
restrictions.
- Asset lifetime, especially for the old connection.
Further, Liemberger [6] showed that the water
losses as percentage of system input did not
represent the performance of water losses
management. Table 1 showed utilities with less than
15% real losses, which was obviously considered that
real losses up to 15% indicate a reasonable leakage
management performance. Taking as examples
Vienna Water Works (Austria) and Ecowater (New
Zealand), whose real losses are between 8 and 9%,
ILI comparison showed that Ecowaters’s leakage
management performance was 6 times better than
Vienna’s. [6]
Conversely, it is not always the case that utilities
with CARL of more than 15% have poor leakage
management. Table 2 shows the 10 best-performing
utilities with ILIs below 4 but their CARL represent
between 6.0 – 24.2 % of their system input.
Table 1. ILI in the Utilities with Real Losses less than 15%
Utility Country
CARL,
% system
input
ILI
SA Utility 20
SA Utility 6
Vienna
Ecowater
SA Utility 13
SA Utility 26
Wide Bay Water
Water Board of Lemesos
SA Utility 1
South Africa
South Africa
Austria
New Zealand
South Africa
South Africa
Australia
Cyprus
South Africa
6,0
7,6
8,5
9,1
9,7
10,1
11,5
12,5
13,2
1,9
2,6
6,0
0,9
1,8
3,8
1,2
1,0
6,2
Source: Liemberger [6]
Table 2 Percentage Water Losses in the Utilities with ILI
less than 4,0
Utility Country ILI
CARL,
% system
input
Ecowater
Water Board of Lemesos
Wide Bay Water
Malta WSC
SA Utility 13
Bristol Water Plc
SA Utility 20
SA Utility 6
Charlotte County Utilities
SA Utility 26
New Zealand
Cyprus
Australia
Malta
South Africa
England
South Africa
South Africa
USA
South Africa
0,9
1,0
1,2
1,6
1,8
1,9
1,9
2,6
3,1
3,8
9,1
12,5
11,5
19,7
9,7
16,8
6,0
7,6
24,2
10,2
Source: Liemberger[6]
Figure 5 shows the leakage management
performance of 30 utilities using the ILI and the
respective losses expressed as percentage of total
Figure 5. ILI vs Real Losses using Data Set of 30 Utilities (on logarithmic scale). [6]

Winarni, W. / ILI as Water Losses Indicator / CED, Vol. 11, No. 2, September 2009, pp. 126–134
134
system input. It is obvious that there is no
correlation, for example 50% real losses mean in one
case an ILI around 12 and in another case 114. This
chart confirms that lower level of real losses say 10%
is not necessarily an indication for good real losses
management.
Data collected in Figure 5 also shows that the
highest calculated ILI was 278, in Dushanbe, the
capital city of Tajikistan. However, water consumption
in this city is extremely high, so the real losses only
represent 16.2 % of total system input. The ILI of
278 sounds unrealistic high, but in individual areas
in Selangor, Malaysia, ILI values of up to 485 was
observed (average 88) since there is no attention and
repairement of burst pipe for years. [9].
Conclusions
The different terminology, calculation methods, and
variety of water balance and Non-Revenue Water
performance indicators limit the possibilities for
benchmarking the true performance. The IWA has
developed a standard international water balance
structure and terminology. This standard format has
meanwhile been adopted by national associations in
a number of countries. It always worth to try to
establish a water balance, even if main elements are
based on estimates.
It is expected that this paper can convinced
managers of water utilities with still high (or
unknown) level of water losses that the
establishment of water balance will be an important
first step towards more efficiency.
It is obvious that the comparison of leakage
management performance between utilities should
not be based on percentage of system input volume.
Since it is influenced by consumption and does not
take into account the factors of supply continuity,
mains length, number of service connections,
location of customer meters, and average operating
pressure. The decision makers, policy makers, and
top management of water utilities should be aware
of the weakness of using term of NRW as percentage
of system input volume.
Accurate performance indicators should be used for
benchmarking, international performance comparison,
target setting or contractual target for internationally
funded project/private sector participation.
The Infrastructure Leakage Index (ILI) is a new
performance indicator for real losses, which
measures the ratio of current annual real losses to
system-specific unavoidable annual real losses. It is
the ideal indicator for making international
comparison. The ILI approach provides an improved
basis for technical comparisons of leakage
management performance which separates aspect of
infrastructure management; repair, pipe and assets
management, effectiveness of active leakage control
policy, from aspects of pressure management.
There is no correlation between ILI and NRW as
percentage of system input volume. Low percentage
of NRW is not necessarily an indication for good real
losses management.
References
1. Alegre H., Hirnir W., Baptista J.M., and Parena
R., Performance Indicators for Water Supply
Services, IWA Manual Best Practice, first edition,
IWA Publishing, London, 2000.
2. Liemberger R. and Farley M., Developing a Non-
Revenue Water Reduction Strategy, Part 1:
Investigating and Assessing Water Losses, Paper
to IWA Congress, Marrakech, 2004. (download
from www.liemberger.cc).
3. Lambert A.O., Brown T.G., Takizawa M., and
Weimer D., A Review of Performance Indicators
for Real Losses from Water Supply Systems,
AQUA, 48 (6), ISSN 0003-7214, 1999, pp. 227–
237.
4. Lambert A.O. and McKenzie R.D., Practical
Experience in using the Infrastructure Leakage
Index, Paper to IWA Managing Leakage
Conference, Cyprus, 2002. (download from
www.liemberger.cc).
5. Lambert A.O., International Report on Water
Losses Management and Techniques: Report to
IWA Berlin Congress, October 2001, Water
Science and Technology: Water Supply, 2 (4),
ISSN 1606-9749, 2002, pp. 1–20.
6. Liemberger R., Do You Know How Misleading
the Use of Wrong Performance Indicators can
be?, IWA Managing Leakage Conference, Cyprus,
2002. (download from www.liemberger.cc).
7. Farley M., Non-Revenue Water–International
Best Practice for Assessment, Monitoring and
Control, 12th
8. Pearson D., Testing the UARL and ILI Approach
Using a Large UK Data Set, IWA Managing
Leakage Conference, Cyprus, 2002. (download
from www.liemberger.cc).
Annual CWWA Water, Wastewater
& Solid Waste Conference, Bahamas, 2003.
(download from www.liemberger.cc).
9. Preston S.J. and Sturm R., Use of the
Infrastructure Leakage Index (ILI) in Malaysia,
IWA Managing Leakage Conference, Cyprus,
2002. (download from www.liemberger.cc).