Infrastructure Leakage Index
(ILI)
as a Regulatory and Provider
Tool
David Michael Delgado Advisor: Kevin Lansey.
Department of Civil Engineering & Engineering Mechanics College of Engineering
Acknowledgement: University of Arizona, Technology and Research Initiative Fund 2007/2008, Water Sustainability Graduate Student
1 Project Relevance
In many water distribution systems a significant percentage of water is lost as leakage while in transit from wells or treatment plants to consumers. Water losses can be categorized as apparent and real. Apparent losses are those that are not accounted for due to poor metering, pirating or use, such as for construction purposes. Real losses are leakage from pipes or connections. A Metropolitan Water study indicated that these losses total approximately 5% of their pumping (Hill and Davis, 2005).
Leakage from pipe and connections can be represented as reported bursts, unreported bursts and background losses. Reported bursts correspond to pipe failures, that are typically large but of short duration. Most of these events can be identified relatively quickly due to pressure changes monitored by the utility, or by water on the ground surface. Unreported bursts have smaller leakage magnitudes and depend on active leakage control to be detected, as leaked water is not seen or cause a nuisance. Background leakage is characterized by small non visible leaks that are usually smaller then 1 gal / min. Background leaks occur mostly at joints and fittings and run continuously, but not generating sufficient noise to be detectable by existing equipment.
Leakage from water distribution system infrastructure is in large part lost to the atmosphere as evaporation or transpiration. Real losses can be reduced through pressure reduction, leak detection field studies and pipe/connection replacements. A 30% reduction in real losses would amount to real decrease of total pumping of between 1-2%. This is equivalent to reducing 5 days of annual water use and the associated treatment and pumping costs. Few other water management issues so directly affect this large of a proportion of the supply and are as potentially controllable.
To achieve these gains, we must quantify water distribution system losses. Arizona Dept of Water Resources (ADWR) requires reporting the percentage of lost and unaccounted for water and limits that amount to 10% of the total pumping. However, no water budget methodology has been explicitly defined so water utilities use a range of definitions for these terms. These inconsistencies can be avoided by applying the infrastructure leakage index (ILI).
The ILI is defined as the current annual real losses (CARL) divided by the unavoidable annual real losses (UARL). The UARL represents the lowest technically achievable annual real losses for a well-maintained well-managed system and is the likely lower bound on water losses. As a performance indicator (PI), the ILI represents a measure of the combined performance of three infrastructure management methods for real losses - the speed and quality of
repairs, active leakage control and assets management – under a certain average operating pressure (Figure 1).
The ILI was introduced in 2000 (Alegre et al) and has been quickly adopted around the world. The ILI approach was tested several years by the IWA Water Losses Task Force; and it is already included in the IWA as a Best Practice Performance Indicator. The American Water Works Association is proceeding to include the ILI as a recommended water audit method (AWWA, 2006). California and Texas are analyzing the ILI as a possible change to their best management practices (Dickinson, 2005). The ILI provides information to regulators to better control leakage losses and to utilities on how to most efficiently apply resources to reduce leakage.
The first step towards computing the ILI is to obtain a water balance. Figure 2 shows the IWA’s “best practice” standard water balance. This water balance table allows reaching a meaningful assessment of volumes of annual real losses (or CARL). Besides the ILI, IWA’s Manual of Best Practice has other recommended performance indicators. According to Liemberger and Farley (2004), Financial and Operational PIs can be can be categorized at different levels as follows:
Level 1 (Basic): a first layer of indicators that provide a general management overview of the efficiency and effectiveness of the water undertaking.
Level 2 (Intermediate): Additional indicators, which provide a better insight than the Level 1 indicators; for users who need to go further in depth.
Level 3 (Detailed): indicators that provide the greatest amount of specific detail, but are still relevant at the top management level. The ILI is the IWA “best practice” level 3 (detailed) PI for Operational Management of Real Losses.
Although “percentage of volume” indicators, like the Unaccounted for Water measure (UFW), have traditionally been accepted as PIs, they can be very misleading as they are strongly influenced by differences and changes in the volume of consumption. IWA’s Manual of Best Practice still recommending “percentage of volume” measures, like the UFW, as a Basic (Level 1) Financial PI for Non-Revenue Water. Nevertheless it should definitely not be used for assessing any aspect of operational performance management of water losses (IWA Task Force, 2000).
An important result from previous studies of the ILI is that the “Real Losses as percentage of volume” measure (RLPV) is not directly correlated with the ILI. For example, see the ILI values for the cities listed in Table 1. Observing Vienna and Lemesos, is possible to notice that Vienna has a lower RLPV and a larger ILI
when compared to Lemesos. Considering that the average supply in Vienna is much larger than in Lemesos and assuming that supposedly these cities have exactly the same supply system (same water losses): Vienna apparently has a smaller real loss according to RLPV, when actually Lemesos is the one who has a smaller real loss (ILI ~ 1). The problem resides on the fact that RLPV is strongly influenced by the system demands, while the ILI is a better indicator since it is based on the system physical configuration.
In addition, considering Makkah in Saudi Arabia (Table 1), over 30% of water is lost to leakage. Losses from most utilities should be significantly less but, for perspective, an 8% leakage loss is equivalent to losing the one month of supply per year. Real losses through pressure reduction could correspond to about 30%, or a real decrease of between 1-2% of total pumping. This is comparable to reducing 5 days of annual water use and the associated treatment and pumping costs.
The proposed project objective is to study the appropriateness of the ILI in Arizona. The primary task is to collect data to compute the ILI for several Arizona water purveyors. Thirteen utilities have agreed previously to participate on this research by providing data from 2000 to 2007 for entire system or by pressure metered zone (PMZ). To provide a mechanism for further applications, an ILI calculation computer program or spreadsheet will be developed.
Comparison of ILI values for the water distribution systems and subsystems will be conducted for systems with varying ages and pipe construction materials. Several components in the ILI are utility estimates, but field studies can fine tune these values. Thus, detailed water loss analyses will be conducted to measure system leakage and evaluate losses during pipe breaks. The ILI provides a means to quantify leakage losses and identify major loss categories. The final task in this project is to identify techniques to reduce those losses. The approach will vary between systems so, based on literature publications and engineering analysis, guidelines for identifying appropriate leakage reduction measures will be developed.
The starting point of this project will regard the collection of sufficient data to compute the ILI for several Arizona water purveyors serving more than 5000 connections (the lower bound of acceptable implementation of the ILI). In addition to basic historic use data, the utilities will be asked to identify any leak reduction measures implemented during that period and their timing. The ILI time series will be computed and analysis of the resulting indices will be performed including temporal trends in the ILI, impacts of leak reduction measures on the ILI and their cost efficiency, correlations between the ILI, percentage indicators and other indices, correlations between the ILI and system
size, age, and pipe materials, and others relationships that appear during the analysis.
Several spreadsheets are available to calculate the ILI including Benchleak (McKenzie and Lambert, 2002) and Aqualibre (Liemberger and McKenzie, 2003). The AWWA has also developed a water audit spreadsheet that allows not only to obtain the system’s water balance, but also to compute many PIs. The model that fits best with the project needs should be chosen or our own model will be developed. This task will be brief, but insure that we have an acceptable tool for Arizona utilities.
The ILI is a global measure and requires several assumptions on the distribution of water losses. The next major task will attempt to reduce the uncertainties in those estimates through more detailed study. These analyses are time consuming and will be focused to a limited set of utilities. The IWA Real Losses Task Force recommends that an alternative calculation of real losses should be carried out to check the results derived from the water balance. To improve these estimates an independent analysis called Night Flow Analysis (NFA) will be performed. The NFA begins by examining system inflows during the lowest demand hours and estimating the proportion that is leakage. These losses are a function of the system pressure and can be represented in hydraulic models. A full day hydraulic analysis can be used to predict the total nightly and diurnal variation of leakage. The results from estimates from night flows will be compared with those computed previously using ILI. If discrepancies result, additional study or assessment is must be completed.
As noted, the ILI can be used to assess the need for and results from a utility conservation plan, and to identify cost effective leak management schemes. The IWA recommends an ILI of 1 to 2 for regions that have limited supplies and few new water sources. For proper application of the index, the ADWR must determine the magnitude of ILI that requires alternative action levels. This study will begin to provide ADWR with guidance to suggest an acceptable value.
2 Methods
To control distribution system losses, most state regulatory agencies, including Arizona, allow a percentage of water delivered or supplied to be unaccounted for or lost. In Arizona a maximum of 10% of the pumped water volume can be unaccounted for or lost. This performance index is not appropriate as it relates the losses to the volume pumped allowing larger users to have larger losses. In addition, unaccounted for water (UFW) is intended to represent leakage but may also include many non-metered uses including fire and construction demands. To overcome these discrepancies, the International Water Association (IWA) has developed an alternative infrastructure leakage index (ILI). The ILI is defined as the current annual real losses (CARL) divided by the unavoidable annual real losses (UARL). The UARL are the lowest technically achievable annual real losses for a well-maintained well-managed system and is the likely lower bound on water losses.
UARL CARL
ILI =
Once obtained the performance indicators (PIs), including the ILI. Alternative calculation of real losses can be assessed by performing the Night Flow Analysis (NFA).
2.1 Water Audit
The procedure to compute the ILI and other PIs start by obtaining the water balance (or water audit). The water balance recommended by IWA and adopted by AWWA is shown on Figure 2. There are four basic steps to build this table:
Step 1) Determine system input volume
Step 2) Determine the authorized consumption Step 3) Estimate apparent losses
Step 4) Calculate the current annual real losses (CARL)
The spreadsheet distributed to participants with the data sets necessary to build the water balance are shown on Figure 3. The first step is to obtain the total volume of water input to the system from own sources and its adjustment by considering estimates of over-registered or under-registered master meter errors. In addition, the bulk water purchased (water imported) and the bulk water sold and conveyed out of the WDS should be respectively accounted and discounted from the adjusted volume form own sources resulting in the water supplied.
To determine Authorized Consumption is necessary to obtain the volume of metered consumption (billed and unbilled) from registered customer meters, and also estimates of unmetered consumptions (billed and unbilled). Authorized Consumption should include items such as fire fighting, flushing of mains and sewers, street cleaning, etc and also consumption from institutions free of charge and from the water utility itself.
Water losses consist of apparent losses and real losses and are estimated subtracting the Authorized Consumption from the Total system input. Apparent losses constitute the most difficult approximation because evolves the estimation of unauthorized consumption, customer meter inaccuracies, and also data handling errors from meter reading and billing system. The real losses correspond as the remainder from the apparent losses subtracted form the water losses and correspond to the Current Annual Real Losses (CARL) in the numerator of the ILI equation. From these water balance table is possible to compute not only ILI but also many other alternative PIs.
2.2 Alternative Performance Indicators
The traditional performance indicator (PI), unaccounted for water (UFW), has been extensively computed by water utilities worldwide. However, any percentage of system input volume measure, including the UFW, is considered as being unsuitable for assessing any aspect of operational performance management of water losses. This conclusion has been sanctioned by many organizations throughout the world, including AWWA. This is because values as percentage of system input volume are strongly influenced by consumption, do not distinguish between apparent and real losses and also, are difficult to interpret in situations of intermittent supply. Nevertheless, Non Revenue Water (NRW) is IWA’s new term for unaccounted for water and is recommended as a Level 1 (Basic) Financial PI:
Supply Losses
UFW =
An operational PI commonly used by providers is the “gallons per service connection per day”. It is considered as a basic PI for IWA for systems with more than 32 service connections / mile of mains. It has some advantages if compared to “gallons per mile of mains per day” because distribution losses expressed in gal/ conn/ day are less influenced by density of connections than losses expressed in gal/ mile of mains / day (Lambert and McKenzie, 2002).
This basic PI is considered the most robust of the traditional evaluators but has certain limitations, as it does not account for mains length, customer meter location (distance between curbstop and customer meter) or average operating
pressure of the system. The latter is an important factor considering that leakage rates vary approximately linearly with pressure for systems with mixed pipe materials.
Trying to address these deficiencies, IWA developed a detailed operational PI for real losses referred to as the Infrastructure Leakage Index (ILI). The ILI measures how effectively a utility is managing real losses under the current operating pressure regime (IWA Task Force, 2000). It also provides more meaningful bases for benchmarking and target setting.
Other PIs like real losses as percentage of total volume input, apparent losses as percentage of total volume input, gal per connection per day per pressure can also be computed. Table 2 shows a list of Financial and Operational PIs for Basic, Intermediate and Detailed levels according to Liemberger and Farley (2004). 2.3 Infrastructure Leakage Index (ILI)
The ILI is the ultimate PI to assess the operational management of real losses and it is considered by IWA “best practice” as a Level 3 (detailed) Operational PI. As mentioned before, the ILI is defined as the current annual real losses (CARL) divided by the unavoidable annual real losses (UARL). The CARL is obtained from the IWA water balance standard. Methods to compute UARL will be addressed later on.
According to Lambert and McKenzie (2002), the equation to calculate UARL was developed and tested by IWA water losses task force and it represents the summation of the real losses volumes from leakage on mains, leakage on service connections, pipe breakages and storage tank overflows. The typical volume lost from each event is the product of the average target duration and the typical flow rates for leaks on mains and service connections. These components were collected from several countries, assuming a well maintained infrastructure in good conditions.
The user friendly version of the UARL equation is:
UARL = (5.41 x Lm + 0.15 x Nc + 7.5 x Lp) x P
Where:
Lm = Length of mains
Nc = Number of service connections Lp = Length of private pipe
P = Average pressure
2.3.1 Interpreting ILI results
Providers have traditionally been used “percentage by volume” PIs to assess many components of the water balance (e.g. UFW or NRW), however, it is an imprecise indicator, as it is strongly influenced by changes in the volume of consumption. ILI is a non-dimensional and an instance will be described in order to help clarifying the meaning of it.
If a certain system has ILI equal to 2, that means that CARL is estimated as being 2 times as high as the minimum expected amount of leakage for a well managed and well maintained system, operated under a certain average pressure. To reduce CARL, and consequently ILI, providers should attempt to improve the speed and quality of repairs, introduce active leakage control and apply good asset management. Additional changes in real losses would result from changes in the pressure management regime.
Nevertheless, ILI lower than 2 is already considered “world class” leakage management according to IWA standards, therefore a cost effective study should be performed before trying to lower these values. In addition, such low ILI values are only likely to be economically justified in regions where water is exceptionally expensive (e.g. desalinization) or water resources are scarce, or both.
2.3.2 Benchmarking
The ILI has the capability of allowing benchmarking in different levels. Comparisons can be carried out by benchmarking different utilities. Also, benchmarking within utilities is possible by analyzing the ILI overtime or evaluating their pressure zones or sub systems.
2.3.3 ILI limitations
Even though ILI has been computed in an increasing number of countries, its usefulness has not been tested for and cannot be recommended with confidence for systems with:
- Less than 5000 connections
- Less than 35 PSI pressure on average, throughout the system - Less than 32 conn / miles of mains
2.4 Pressure Management
There is a physical relationship between leakage rate and pressure. This relationship can be assumed linear for large systems with mixed materials and
for WDS using plastic pipes leakage rates vary approximately with pressure to the power 1.5. All metal pipe systems are predominantly pipe breakage leakage and are subject to high leakage rates and power exponents close to 0.5.
Therefore, pressure management plays an important role in controlling real losses. If pressure is reduced, the rate of increase in leakage will reduce. According to Liemberger and Farley (2004), some tasks should be assessed to evaluate the appropriateness of pressure management on a certain part of the system or pressure zone:
- Identifying potential pressure zones, installation points and customer issues
- Demand analysis to identify customer types and control limitations
- Logged 24 hours flow and pressure measurements at inlet, average zone point and critical point
- Perform a pump test
- Asses Night Flow Analysis and Leakage Modeling - Identify correct check valves and PRVs
- Cost benefit analysis
It is important to note that this does not imply that the pressure management is optimal – it is usually possible to reduce the volume of real losses (but not the ILI) by improved active pressure management.
2.5 Night Flow Analysis
The ILI and other PIs are a global measure and requires several assumptions on the distribution of water losses. Errors in the measured or estimated components input to the calculation result in errors in the components of real losses. Night Flow Analysis (NFA) is an alternative calculation of real losses to check values derived from the water balance and will attempt to reduce the uncertainties in those estimates through a more detailed study.
Night Flow Analysis (NFA) helps determining the level of leakage in a particular zone metered area. NFA starts by collecting hourly pressure data for zone, measuring pressure and flows at the zone inlet and also the logged pressures at the average and critical points.
The next step is to estimate the minimum domestic and non-domestic hour usage. Domestic night use can be assessed by simply considering the population active at night (usually assumed as 6%) multiplied by their consumption, which is mostly flushing the toiled at night.
The small non-domestic night use is more difficult to evaluate and depends to a large extent on the type of businesses being run in the pressure metered zone. To facilitate this estimation, users are lumped into various categories and a typical night use is assumed for each group. For example, there may be several all-night convenient stores where the unit use is relatively small although when added together the total use may be significant. Large non-domestic users like airports, large hotels, breweries, swimming pools, etc should be metered individually.
Considering the Pressure / distribution losses equation:
1 0 1 0 1 N P P L L ⎟⎟ ⎠ ⎞ ⎜⎜ ⎝ ⎛ = Where:
L0 = initial leakage loss in gal/h
L1 = new leakage loss in gal/h
P0 = initial pressure (PSI)
P1 = new pressure (PSI)
N1 = pressure exponent (non-dimensional)
The N1 value used in the equation represents the power exponent for all distribution losses in the system which is influenced by pressure.
According to SANFLOW (2001), the value for N1 used normally vary between 0.5 (default value for bursts) and 2.5 (highest value for background leakage) with an average or default value of 1.0. Systems with a high percentage of background leakage will tend to have N1 values in excess of 1.0 while systems where the leakage is predominantly burst leakage on iron or steel pipes will have N1 values of less than 1.0.
If possible, the value of N1 for a system should be calculated directly using measured information obtained from a “pressure step-test” analysis (pump test) undertaken during the period of minimum night flow. The pressure step-test analysis may take between two and three hours during which the minimum night flow would normally remain relatively constant.
Once the field data is collected, Night Flow Analysis and a 24 hour leakage modeling can be evaluated. The South African Night Flow Analysis Model (SANFLOW) described by Mackenzie and Bhagwan (2004), is an example of a model designed to provide an indication of the unexplained burst leakage in a zone from the analysis of the minimum night flow analysis.
3 Key Findings
The study case included on this research focused on the evaluation of water losses in water distribution systems in the state of Arizona, using alternative performance indicators, mostly the Infrastructure Leakage Index or the ILI.
The aim is to conduct ILI analyses for a number of Arizona water providers, performing multi-year analyses. Also, a comparison between the UFW measure currently in use by ADWR and ILI is performed. Moreover, a Night Flow Analysis (NFA) is assessed in a limited number of systems. In addition, uncertainty analysis is being performed on the components with larger uncertainty. Finally, the project should provide feedback to participants and ADWR on alternative PIs and ILI as potential provider tools.
13 AZ providers committed on participate on the project by providing spreadsheet data from 2000 to 2007 for entire system or by pressure zone. 3 AZ utilities had their PIs and ILI assessed. Night Flow Analysis will be performed in only 3 AZ providers. Utilities will be always referred as anonymous data sets. At the end on this project, participants will receive a report with a summary of the results.
3.1 ILI in Arizona
Since the ILI corresponds to the most powerful indicator for assessing the efficiency of the operational management of real losses, benchmarking and target setting, therefore the focus on this project is on this PI.
Figure 4 shows ILI values collected from 7 water utilities in North America and from the three AZ water utilities. Is possible to notice that providers “AZ 1” and “AZ 2” show not only a smaller ILI when compared to the other utilities, but also demonstrate that their ILI values are below 2.
IWA recommends ILI 1-2 for regions that have limited supplies and few new water sources and Figure 5 correlates the ILI within this Technical Performance Category. According to this figure, ILI between 1-2 corresponds to Category A, which means that these two water utilities have good performance in respect to real losses. Nevertheless, provider “AZ 3” has ILI above 8. According to the real loss target matrix, “AZ 3” shows poor conditions in respect to real losses performance; therefore leakage management methods should be prioritized in order to improve conditions of this provider.
3.2 Benchmarking and Target Setting
As mentioned on the previous chapter, ILI can be used for benchmarking in different levels. Comparisons can be assessed by benchmarking utilities, and within utilities, by benchmarking sub-systems or comparing the ILI overtime. Figure 6 is an instance of a benchmarking performed over time within the water utility “AZ 2”. This provider was evaluated between 2000 to 2006 and it presents average ILI lower than 2. A reduction can be noticed on this PI during the years of 2002 and 2004 because the speed and quality of repairs and the infrastructure management overall were improved during these years.
This same figure also illustrates ILI decreased in 2005, this is due to the delivery of reclaimed water and, as a result, a less usage of the potable water supply and consequently, less real losses from the potable system.
The Non-revenue Water as a percentage of water supplied (NRW by volume) from provider “AZ 1” was assessed and the results are shown in Figure 7. This Basic Financial PI increased during 2004 and 2005 because the NRW increased on a larger step then the water supplied, however a drop from 2006 to 2007 can be noticed due to a significant reduction in the unbilled authorized consumption. Benchmarking of sub-systems within water utilities are demonstrated at Figures 8 and 9. Figure 8 presents the Annual Cost of Real Losses by each pressure zone of “AZ 1” provider. The benchmarking of subsystems within the water utility can aid operators and practioners evaluating if it is worthwhile to invest money in real losses reduction actions, also indicating which parts of the system have needs urgent care.
Figure 9 shows a Basic Operational PI for real losses - by gallons per service connections per day. It is considered the best of the basic PIs and can be used for target setting. Figure 10 presents the real loss target matrix. This figure allows matching average operating pressures and the correspondent leakage (real loss) at each pressure zone.
Analyzing the results from Figure 9 together with the real loss target matrix (Figure 10) is possible to observe that Zones 1, 2 and 5 have good performance in respect to real losses, because they fall on the Technical Performance Category A. However, Zones 3 and 4 fit into Category B, and should consider pressure management or any infrastructure management practices in order to reduce the real losses. Zone 5 shows poor conditions in respect to real losses performance. Leakage management methods should be prioritized in order to improve conditions of the PMZ.
3.3 Sensitivity Analysis
Any errors in the measured or estimated components input to the water balance table, especially at the unmetered consumptions and apparent losses estimations, end up as errors in the real loss estimation. Sensitivity analysis was then performed in order to reduce the uncertainty in some components of the water balance table. Uncertainties were considered on the average operating pressure and real losses terms. Figures 11 and 12 show the sensitivity of the UFW and ILI and a following comparison between them.
The first sensitivity analysis assumed a variation between 100 to 200 % of real losses. Figure 11 shows that UARL was kept constant. This is because the system configuration and pressure was assumed constant. Therefore, changes in ILI increased from 1.88 to 3.76, while UFW varied from 6.1% to 11.6%. Again, these results demonstrate that ILI and UFW are not necessarily correlated, and also show that UFW is imprecise because it is demand driven.
Figure 12 illustrates a variation between 80 to 120% in the average operating pressure of the anonymous water utility “AZ 2”. UARL varied this time because changes in the operating pressure resulted in changes in this component. ILI kept constant in 1.88, however UFW varied from 6.1 to 7.4%. These results shown the importance of considering the operating pressure in the PI and also shows that real losses analysis should be based on systems physical configuration and not demand driven (e.g. UFW).
3.4 Night Flow Analysis
Night Flow Analysis can help not only evaluating the degree of leakage on a certain part of the system, but also can aid reducing the uncertainty in the real loss measures. After collecting field data and performing the so called pump test, a 24 hour leakage modeling can be assessed. The SANFLOW and PRESMAC programs (WRC, 2004) assisted obtaining the 24 hours leakage modeling results and generating plots.
Field data was collect from a pressure metered zone (PMZ) at provider “AZ 3”. Logged pressures were collected at the inlet point, at the average zone point and at the critical point. The critical point corresponds to the highest topographic location of the system, or the farthest location from the source. The inflow at the inlet point was also recorded.
Background leakage values were assumed from standards that depend on pipes materials and system age. Domestic consumption was obtained from the total population supplied by this sub-system. There was only one small non-domestic user and any large non-domestic user in the PMZ.
A pump test could not be performed; however, as can be noticed in Figure 13, the PMZ does not have any significant change on the pressure during the 24 hour analysis.
The 24 hour leakage modeling is represented in Figure 13. The red line is the total inflow to the zone, which corresponds to the consumption and leakage (background leaks and unreported bursts). The green line represents the consumption while the pink line is the leakage. Note that consumption varies together with inflow (“pressure independent”). In the other hand, leakage varies with pressure (“pressure dependent”).
The area below the pink line represents the extent of leakage in this sub-system. However, it is often convenient to express the leakage in terms of equivalent service pipe bursts. An equivalent service pipe burst is generally taken to be approximately 422 gal/ hour. The number of equivalent service pipe bursts on this zone corresponds to 18. These results demonstrate that the current PMZ needs imperative actions towards real losses reduction.
The Night Flow Analysis provides a more detailed analysis of the real losses, and it also helps identifying if leak detection programs should be initiated. NFA also allows a more accurate estimation of ILI.
4 Conclusions
The project demonstrated that ILI is an improved water balance measure to water providers and ADWR. This study also shown that UFW is an imprecise PI, as it is strongly influenced by differences and changes in the volume of consumption. In addition, UFW should not be used for assessing any aspect of operational performance management of water losses.
ILI also proved to represent a more meaningful basis for performance comparisons, benchmarking, target setting and analysis. In addition, the ILI could be used to assess the need for and results from a utility conservation plan, and to identify cost effective leak management schemes.
This research aimed to quantify water utilities system losses, demonstrating real losses breakdown by NFA and leakage modeling. Future research could include guidelines to specify which alternatives, including pipe and valve replacement, leakage detection programs, setting up pressure reducing valves and optimized pump operations, would represent the optimal real loss reduction for Arizona providers.
Finally, case ILI is accepted by ADWR is necessary to define what would be the maximum allowable ILI for Arizona.
5 References AWWA. (2006).
http://www.awwa.org/WaterWiser/waterloss/Docs/03IWA_AWWA_Method.cfm Alegre, H. Hirner, W., Bapista, J., and Parena, R. (2000). “Performance indicators for water supply services” IWA Manual of Best Practices, ISBN 900222272.
Dickinson, M. (2005). “Redesigning water loss standards in California using the new IWA methodology”, paper presented at Leakage 2005, Halifax, Canada (available at http://www.leakage2005.com/).
Hill C., and Davis, S. (2005). “Economics of Domestic Residential Water Meter Replacement Based on Cumulative Volume”, powerpoint presentation for Tucson Metro Water, Tucson, Jun.
IWA Task Force, 2000, Best Practice Performance indicators: a practical approach.
Lambert, A and McKenzie, R. (2002) “Practical Experience in using the Infrastructure Leakage Index.” Paper to IWA Conference ‘Leakage Management – A Practical Approach’, Cyprus, November 2002, (download from
www.liemberger.cc)
Liemberger, R. and Farley, M. (2004). “Developing a non-revenue water reduction strategy”, powerpoint presentation from the IWA Congress, Marratech, Sept.
Liemberger, R. and McKenzie, R. (2003). “Aqualibre: a new innovative water balance software”, presented at the IWA/AWWA conference on efficient management of urban water supply, Tenerife.
Mackenzie, R., Bhagwan, J., “Introduction to WRC Tools to Manage Non-Revenue Water”, 2004.
McKenzie, R. and Lambert, A. (2002). Benchleak User Guide, Water Research Commission Report, TT 159/01.
WRC. (2004), http://www.wrc.org.za/publications_reports3.htm
APPENDIX
Table 1 – Comparing ILI and UFW (modified from Liemberger and Farley, 2004). City Real loss (as percentage of volume) ILI Vienna 9 6 Lemesos Cyprus 13 ~1 Bristol 17 1.9 Philadelphia 26 ~14
Makkah, Saudi Arabia 32 >70
Table 2 – Recommended Performance Indicators (modified from Liemberger and Farley, 2004).
Function Level
Financial: 1
NRW by Volume (Basic)
Operational: 1
Real Losses (Basic)
Operational: 2
Real Losses (Intermed.)
Financial: 3
NRW by Cost (Detailed)
Operational: 3
Real Losses (Detailed)
[gal / miles of mains / day / PSI] (only if connection density is < 32 conn. / mi)
Value of NRW
[as % of annual cost of running system] Infrastructure Leakage Index (ILI)
or:
[gal / miles of mains / day]
[gal / conn. / day / PSI] or:
(only if connection density is < 32 conn. / mi) Performance Indicator
Volume of NRW
[as % of System Input Volume] [gal / conn. / day]
Figure 1 – The four basic methods of managing real losses (from Lambert and McKenzie, 2002).
Figure 2 – Standard IWA Water Balance (from IWA Task Force, 2000).
Legend ACC / ADWR Annual Reports Estimated data Missing data
Water Supplied 2000 2001 2002 2003 2004 2005 2006
Volume from own sources MI gal/ yr 95,526.0 95,526.0 95,526.0 95,526.0 95,526.0 95,526.0 95,526.0
Master meter error % 2.0 2.0 2.0 2.0 2.0 2.0 2.0
Water imported MI gal/ yr 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Water exported MI gal/ yr 7,210.2 7,210.2 7,210.2 7,210.2 7,210.2 7,210.2 7,210.2
Authorized Consumption 2000 2001 2002 2003 2004 2005 2006
Billed Metered MI gal/ yr 57,535.2 57,535.2 57,535.2 57,535.2 57,535.2 57,535.2 57,535.2
Billed Unmetered MI gal/ yr 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Unbilled metered MI gal/ yr 179.3 179.3 179.3 179.3 179.3 179.3 179.3
Unbilled Unmetered MI gal/ yr 693.6 693.6 693.6 693.6 693.6 693.6 693.6
Apparent Losses 2000 2001 2002 2003 2004 2005 2006
Unauthorized consumption MI gal/ yr 1,145.2 1,145.2 1,145.2 1,145.2 1,145.2 1,145.2 1,145.2
Customer metering inaccuracies MI gal/ yr 162.5 162.5 162.5 162.5 162.5 162.5 162.5
Data Handling Errors MI gal/ yr 2,751.2 2,751.2 2,751.2 2,751.2 2,751.2 2,751.2 2,751.2
System Data 2000 2001 2002 2003 2004 2005 2006
Length of Mains (Transmission + Distribution) miles 3,160.0 3,160.0 3,160.0 3,160.0 3,160.0 3,160.0 3,160.0
Number of Service Connections - 548,289.0 548,289.0 548,289.0 548,289.0 548,289.0 548,289.0 548,289.0
Average Length of Private Pipe ft 12.0 12.0 12.0 12.0 12.0 12.0 12.0
Average operating pressure when system is pressurised PSI 55.0 55.0 55.0 55.0 55.0 55.0 55.0
Population served by the system - 900,000.0 900,000.0 900,000.0 900,000.0 900,000.0 900,000.0 900,000.0
Cost Data 2000 2001 2002 2003 2004 2005 2006
Unit Value of Real Losses (eg bulk purchase price) $/ MI gal 133.58 133.58 133.58 133.58 133.58 133.58 133.58
Unit Value of Apparent Losses (eg selling price) $/ 1000 gal 3.95 3.95 3.95 3.95 3.95 3.95 3.95
Total Annual Cost of operating water system $/ yr 167,604,000 167,604,000 167,604,000 167,604,000 167,604,000 167,604,000 167,604,000 Water Audit
Figure 3 – UA Water Audit Spreadsheet.
0 2 4 6 8 10 12 14 16 In fr ast ru ct u re L eaka g e I n d e x AZ 1 AZ 2 1 2 3 4 5 6 7 AZ 3
Infrastructure Leakage Index (ILI)
Figure 4 – ILI values in America and Arizona (modified from Lambert and McKenzie, 2002).
ILI
Horrendously inefficient use of resources; leakage reduction programs imperative and high priority
1 - 2 A
2 - 4 B
4 - 8 C
> 8 D
better active leakage control practices, and better network maintenance Poor leakage record; tolerable only if water is plentiful and cheap; even
then, analyze level and nature of leakage and intensify leakage reduction efforts Technical Performance Category
Further loss reduction may be uneconomic unless there are shortages; careful analysis needed to identify cost effective improvement Potential for marked improvements; consider pressure management;
Figure 5 – ILI target matrix and technical performance category (Modified from Dickinson, 2005). 0 0.5 1 1.5 2 2.5 3 In fr ast ru ct u re L eakag e I n d e x 2000 2001 2002 2003 2004 2005 2006
Infrastructure Leakage Index (ILI)
Figure 6 – ILI - over time benchmarking.
0% 1% 2% 3% 4% 5% 6% 7% 8% N R W ( % of V o lum e ) 2003 2004 2005 2006 2007
Non - Revenue Water (% of Volume)
Figure 7 – NRW - over time benchmarking.
0 2000 4000 6000 8000 10000 12000 14000 16000 Co st o f Real l o sses ( $ )
Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6 Zone 7 Zone 8
Annual Cost of Real Losses
Figure 8 – Annual cost of real losses – Benchmarking by pressure zone.
0.00 20.00 40.00 60.00 80.00 100.00 120.00 g a l/c onn. /da y
Zone 1 Zone 2 Zone 3 Zone 4 Zone 5 Zone 6
Real Losses (gal / conn. / day)
Figure 9 – Real losses (gal / conn / day) – Benchmarking by pressure zone.
Figure 10 – Real loss target matrix and technical performance category (Modified from Liemberger, 2005).
ILI vs. Unaccounted for Water 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 190 210 230 250 270 290 310 330 350 370 390
Real Losses (Mil gal/year)
IL I 0% 2% 4% 6% 8% 10% 12% 14% Unac cou n te d for Wate r ILI UFW
Figure 11 – Sensitivity analysis – uncertainties in the real losses
ILI vs. Unaccounted for Water
0 1 2 3 4 5 6 7 8 9 10 55 60 65 70 75 80 85 90 Pressure (PSI) IL I 0% 1% 2% 3% 4% 5% 6% 7% 8% 9% 10% Un acco u n ted f o r Wat e r ILI UFW
Figure 12 – Sensitivity analysis – uncertainties in the average operating pressure
Leakage Modelling 0.0E+00 1.0E+04 2.0E+04 3.0E+04 4.0E+04 5.0E+04 6.0E+04 09 :0 0 11 :0 0 13 :0 0 15 :0 0 17 :0 0 19 :0 0 21 :0 0 23 :0 0 01 :0 0 03 :0 0 05 :0 0 07 :0 0 Time Fl ow r a te ( g a l / hr ) 0.00 20.00 40.00 60.00 80.00 100.00 120.00 P ress u re ( P S I)
Inflow Leakage Consumption Inlet Pressure
Figure 13 – Night Flow Analysis – Leakage Modeling
