CHAPTER 2 LITERATURE REVIEW
2.7 PERFORMANCE INDICATORS
2.7.1 THE IWA WATER BALANCE
Figure 2.7: The IWA Water Balance (Lambert et al., 2000)
The water balance shown in Figure 2.6 was adopted for use by EWS in 2002 and these figures are calculated monthly and reported on annually. This can be computed using either a top down approach or a bottom up approach depending on the information that is known about the network.
Using the IWA water balance, a Utility can report their status in a competent and standardised manner. Brothers (2003) advises that the term “un-accounted for water” should not be used as standards for its calculation do not exist and no confidence can be given for its accuracy.
2.7.2 INFRASTRUCTURE LEAKAGE INDEX (ILI)
Lambert and Hirner (2000) note that the traditional technical performance indicators for real loss are:
• A percentage of the System Input Volume
• A figure per length of mains per day
• A figure per service connection per day
• A figure per property per day.
Real loss expressed as a percentage of Input Volume (i.e. % NRW) is unsuitable as an indicator because it fails to take the system characteristics into account (i.e. average pressure, number of connections, length of mains, or the time that the system is pressurised). The %NRW is also
System Input Volume
Authorised Consumption
Revenue Water
Non Revenue
Water Billed
Authorised Consumption
Unbilled Authorised Consumption
Apparent Losses
Real Losses Water
Losses
Billed Metered Consumption
Unbilled Unmetered Consumption Unauthorised Consumption Customer Meter Inaccuracies
Leakage on Transmission and Distribution Mains Billed Unmetered Consumption Unbilled Metered Consumption
Leakage on Service Connections up to point of Customer Meter
Leakage and Overflows at Storage Tanks
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influenced by changing customer demand which can cause the percentage of losses to change even though the real loss volume doesn’t change. To overcome this problem and develop an indicator that takes the above into account Lambert and Hirner (2000) reported that the IWA Water Loss Task Force proposed the following:
ILI = TIRL/UARL, where,
TIRL = Technical Indicator of Real Losses
= Current Annual Volume of Real Losses / Number of Connections, and UARL = Unavoidable Average Real Loss,
= (A x Lm/Nc + B + C x Lp/Nc) x P (when system pressurised)
where A=18, B=0.8, C=25, Lm=Length of main (km), Nc=Number of connections, P=Pressure in meters and Lp=Length of service connection from the main to customers meter. In South Africa Lp is taken as 0 because the flow meters are located in the road verge.
The formula for UARL was first published by Lambert et al. (1999) and is defined as the lowest technically achievable volume of real loss for each individual system, assuming infrastructure is in good condition and well-maintained. This equation was developed using BABE (Bursts and Background Estimates) and the FAVAD (Fixed and Variable Area Discharges) relationship between pressure and leak discharges (Lambert, 2010).
Lambert (2010), provides more detail on how the values of Unavoidable Background Leakage (UBL) and UARL are calculated in Table 2.9.
Table 2.9: Parameters values used to calculate UBL and UARL at 50m (Lambert, 1999)
Infrastructure Component
Unavoidable Background Leakage
(UBL)
Detectable Reported Leaks and Bursts
Detectable Unreported Leaks and Bursts
On Mains 20 litres/km/hr
12.4 bursts/100 km/yr.
at 12 m3/hr for 3 days
= 864 m3/burst
0.6 bursts/100 km/yr.
at 6 m3/hr for 50 days
= 7200 m3/burst
On Service Connections, Main
to Property Line
1.25 litres/conn/hr
2.25/ 1000 conns/yr.
at 1.6 m3/hr for 8 days
= 307 m3/burst
0.75/1000 conns/yr.
at 1.6 m3/hr for 100 days
= 3840 m3/burst
On Service Conns from Property Line to
meter, if customer meter is not located
at the property line
0.50 litres/conn/hr*
1.5/ 1000 conns/yr.*
at 1.6 m3/hr for 9 days = 346 m3/burst
* for 15 metres average length
0.50/1000 conns/yr*.
at 1.6 m3/hr for 101 days= 3878 m3/burst
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The units of both TIRL and UARL are litres/connection/day, so the ILI is a non-dimensional index. If a Utility has an ILI=1, it means that the level of real losses is at a minimum and that the system is as close to “perfect” as possible. If a Utility has an ILI=10, this means that their real losses are ten times higher than the minimum value.
Table 2.10: Components of Unavoidable Annual Real Losses (Lambert, 1999)
Figure 2.8: ILI dataset from 27 Countries (Liemberger et al., 2005)
Figure 2.8 shows the original dataset of 27 countries where the ILI was calculated when it was developed, showing a spread of values from 1 to 80.
International Benchmarking
0 10 20 30 40 50 60 70 80 90
0 Australia New Zealand UK UK UK Germany France Czech Rep. New Zealand Japan Ireland Hungary South Africa Czech Rep. Italy Ukraine Greece South Africa Caribbean Sri Lanka Hungary Turkey Italy Greece Costa Rica Bulgaria Jordan Malaysia Indonesia Sri Lanka Turkey Turkey Russia Vietnam
ILI
Infrastructure Leakage Index (ILI)
Randomly Selected International Data Set
0
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2.7.3 WORLD BANK INSTITUTE PERFORMANCE INDICATORS
Using physical losses/connection/day for various levels of pressure, and the Infrastructure Leakage Index (ILI), Liemberger and McKenzie (2005) have developed targets for both developed and developing countries (Table 2.11). As the levels are banded, this gives a simple and rapid basis for utilities to see where they lie and where they should aspire to be.
Table 2.11: World Bank Physical Loss Assessment Matrix (Liemberger et al., 2005)
A well run Utility in a developed country should achieve real loss rates of 5 litres / connection / day per metre of average pressure. The targets for developing countries are half that of developed countries.
According to Liemberger et al. (2005), the interpretation of the Technical Performance Category is given as follow:
“A Further loss reduction may be uneconomic unless there are shortages; careful analysis needed to identify cost effective improvement
B Potential for marked improvements; consider pressure management; better active leakage control practices, and better network maintenance
C Poor leakage record; tolerable only if water is plentiful and cheap; even then, analyse level and nature of leakage and intensify leakage reduction efforts D Horrendously inefficient use of resources; leakage reduction programs
imperative and high priority”
10 m 20 m 30 m 40 m 50 m
A 1 - 2 < 50 < 75 < 100 < 125
B 2 - 4 50-100 75-150 100-200 125-250
C 4 - 8 100-200 150-300 200-400 250-500
D > 8 > 200 > 300 > 400 > 500 A 1 - 4 < 50 < 100 < 150 < 200 < 250 B 4 - 8 50-100 100-200 150-300 200-400 250-500 C 8 - 16 100-200 200-400 300-600 400-800 500-1000 D > 16 > 200 > 400 > 600 > 800 > 1000 Developed Country Situation
Developing Country Situation
Technical Performance Category
ILI
Liters/connection/day
(when the system is pressurized) at an average pressure of:
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Figure 2.9: Australian ILIs for 2005-06 (McKenzie et al., 2012)
It can be seen from Figure 2.10 that the smaller systems (10 000 to 50 000 properties) tend to perform worse than the bigger systems. This trend is also seen in South Africa, where the rural schemes have much higher loss rates. Two contributing factors to this dynamic are that the connection densities of rural schemes are lower and the staff running these supply schemes are not as skilled or resourced as those operating bigger supply schemes (McKenzie et al., 2012).