Apparent Losses

It is important to notice that apparent losses are not caused by leakage. They do not include any physical losses of water, since the water has reached the destination of an end user. However, this successful supply function was inaccurately metered, archived improperly in the billing system, or the use of water was unauthorized. Apparent losses are a very important component for the water supplier to keep under control as they have a direct negative impact on suppliers' revenue generation for...

Developing the Customer Meter Accuracy Testing Program

In order to assess and maintain good physical accuracy of the customer meter population, many water utilities operate their own meter test facility and equipment, and perform ongoing accuracy testing of meters that have been rotated out of service. For these operations, testing of targeted groups of meters can be readily accommodated. Water utilities that do not have their own facilities can outsource their testing to specialty companies. Total customer consumption meter error includes meter...

How Much Water Are We Losing

Throughout the world water losses are occurring at both the end-user's plumbing and the water supplier's distribution piping. Water losses are a universal problem and they do occur in both developed and developing countries. Water loss is defined as occurring in two fundamental ways 1. Water lost from the distribution system through leaking pipes, joints, and fittings leakage from reservoirs and tanks reservoir overflows and improperly open drains or system blow-offs. These losses have been...

References

Performance Indicators for Water Supply Services. Manual of Best Practice. London IWA, 2000. 2. Tardelli, J. Chapter 10. In Abastecimento de Agua. Sao Paulo, Brazil. Tsutiya M Escola Politecnica, Universidade de Sao Paulo 2005. 3. Grigg, S. N. Main Break Prediction, Prevention, and Control. Denver, Colo. AWWARF, AWWA, and IWA, 2005. 4. American Water Works Association. Water Audits and Leak Detection, 3rd ed. Manual M36. Denver, colo AWWA, in press. 5....

Professional

We hope you enjoy this McGraw-Hill eBook If you'd like more information about this book, its author, or related books and websites, please click here. I would like to dedicate this book to my wonderful son and fishing buddy , Nicholas, who came into my life shortly after the release of the first edition of this manual while of course remembering my daughter, Victoria, who since the first edition has grown into a beautiful young woman I would like to dedicate this book to my beloved wife,...

International Experience

The situation in other parts of the world is quite different from England and Wales. Water supply is often still in the hands of local municipal authorities each covering a relatively small number of properties. Most connections are metered, but it is common for supplies to be intermittent due to resource shortages. Sectorization is very rare and proactive leakage control is limited. The benefits of pressure management are not widely appreciated and there is generally no assessment of the...

Top Down Water Balance

The first step in this analytical process of assessing and calculating the volume of real and apparent losses is to undertake a IWA AWWA recommended standardized top-down water balance see Chap. 7 for a detailed guidance on how to undertake a water audit . Good management of any resource requires that the supplier maintain accurate records of transactions and deliveries of the commodity provided to its customers. A water balance has exactly that goal, tracking and accounting for every component...

Calculation of Nonrevenue Water

Definition The difference between system input volume and billed authorized consumption. Nonrevenue water is the portion of the water that a utility places into the distribution system that is not billed and, therefore, recovers no revenue for the utility. Nonrevenue water consists of the sum of unbilled authorized consumption metered and unme-tered , apparent losses, and real losses. It is recommended as best practice by the IWA and AWWA WLCC that the assessment of real losses using a top-down...

The Economic Approach to Apparent Loss Control

Four Pillars Apparent Loss

Figure 11.3 is a graph that represents a conceptual approach to water loss control, in this case applied to apparent losses.6 The center boxes represent three levels of apparent losses, as defined below The outer box represents the current volume of apparent losses that a water utility can quantify using the water audit process. The middle box represents the utility-specific target level for apparent losses. Conceptually, this is the economic level of apparent losses ELAL , or the level at...

Flow Measurement Capabilities of Customer Water Meters

Neptune Compound Water Meters

In general, meter accuracy is influenced by two principal factors the physical performance of the flow sensing mechanism of the meter, and the appropriate sizing of the meter to fit the customer's consumption profile. Water utilities provide service to a wide variety of customers, from residential service 5 8-in meters typically in the United States to large industrial sites up to 12-in meters . Many accurate and reliable meter types exist to measure flows in this variety of settings each with...

The Use of Confidence Limits and Variance Analysis for Water Audits

Statistical Variance

The use of 95 confidence limits to validate the degree of uncertainty in individual components of the water balance is nowadays best practice among qualified water loss management professionals. In order to understand the concept of 95 confidence limits, it is first necessary to understand normal distributions which are an important class of statistical distributions. All normal distributions are symmetric and have bell-shaped density curves with a single peak. To speak specifically of any...

Using BABE Modeling Concepts to Prioritize Activities

It is not recommended that component analysis is undertaken on its own to derive a volume of annual real losses because there is likely to be a significant level of uncertainty Problem-Solving Using BABE and FAVAD Concepts Economic frequency of leakage control Annual water balance and components of losses Night-day factor Pressure management Night-day factor Pressure management Annual water balance and components of losses Figure 10.1 Range of problems which have been successfully modelled...

Determining the System Input Volume

Definition The annual volume input to the water supply system. In case the entire system input is metered, the calculation of the annual system input should be a straightforward task. The regular meter records have to be collected and the annual quantities of the individual system inputs calculated. This includes own sources as well as imported water from bulk suppliers. The accuracy of the input meters should be verified on an annual basis, using portable flow-measuring devices, or if possible...

Assessment of Apparent Losses

Definition This component includes unauthorized consumption, all types of customer metering inaccuracies and data-handling errors. It is difficult to provide general guidelines of how to estimate unauthorized consumption. There is a wide variation of situations and knowledge of the local circumstances will be most important to estimate this component. Unauthorized consumption can include Misuse of fire hydrants and fire-fighting systems, for example, unauthorized construction use of hydrant...

Developing a Revenue Protection Program to Control Apparent Losses

The most significant impact of apparent losses for water utility managers is uncaptured revenue. The label revenue protection program is used to identify the collective activities used to protect the utility's revenue base by controlling apparent losses. As noted above, a number of distinct components, and subcomponents, of apparent losses occur in water utilities therefore a revenue protection program must be tailored to the individual needs of the water utility. Figure 11.76 shows an example...

Network Rehabilitation

Network rehabilitation both mains and service pipes will reduce the rate at which leaks break out on the network. This will reduce leakage, as well as reducing costs associated with inspections and active leakage control activity highlighted above. Figure 9.5 shows a typical burst frequency distribution curve. This shows that there is a distribution of the frequency at which pipes burst on the network. A small proportion will burst Figure 9.5 Burst frequency distribution. Source Dave Pearson...

Unauthorized Consumption

Unauthorized consumption occurs in virtually all drinking water utilities. It typically occurs through the deliberate actions of customers or other persons who take water from the system without paying for it. The nature and extent of unauthorized consumption in a system depends on the economic health of the community and the emphasis that the water utility places on policy and enforcement. Unauthorized consumption occurs in many ways, including tampering of customer meters or meter-reading...

BottomUp Analysis of Real Losses Using DMA and Minimum Night Time Flow Analysis

Iwa Minimum Night Flow

The two ways of assessing real losses explained in the previous sections can be generalized as desktop analysis. However, an MNF analysis uses field test data to quantify the volume of real losses within the distribution network. The results can be directly compared with the volume of real losses obtained from the top-down water balance. A DMA is required in order to conduct MNF measurements. A DMA is a hydraulically discrete part of the distribution network that is isolated from the rest of...

Background

The world's population exploded during the twentieth century. At the close of the year 2000 approximately 6 billion inhabitants called the planet earth home, up from 4 billion in 1974.1 That such growth could occur is a testament to man's unique ability to provide the essentials of clean air, water, food, and health care to its masses. However, during the latter half of the same century, man also recognized that the world's resources couldn't continue to sustain this rate of growth indefinitely...

Current Water Loss Management Practices

Philadelphia Water Loss

The starting point for successfully managing water losses is to accurately assess water supply and consumption volumes by conducting a standardized IWA AWWA water audit. Many water audits are performed by utilities in the United States annually, but they lack uniformity. The audit methods used, the performance indicators and expressions of water losses calculated, and the time intervals between audits vary significantly from utility to utility. The majority of water utilities do not use the IWA...

The Iwaawwa Recommended Standard Water Audit

The top-down water audit is basically assembled in two steps 1. Quantification of all individual water consumption and water loss components, via measurement or component based estimation 2. Undertaking the standardized water balance calculation This section explains the recommended water audit approach and each component of the water audit. The effort required to conduct a top-down water audit is relatively modest depending on the availability and quality of data. The top-down audit also helps...

Modeling Customer Meter Accuracy

Customer meters have been called the cash register of the utility and are responsible for ensuring an equitable distribution of water volume and income throughout various different customer types within a utility. It is therefore extremely important to assess the accuracy of the meters on a regular basis and make repairs or replace groups of meters to keep the customer meter population at an overall high level of accuracy. Accurate metered consumption data is also necessary for engineering...

Data Transfer and Systematic Data Handling Errors

The customer water meter is only the beginning of a sometimes complicated trail that ultimately generates a large amount of customer consumption data. Since most water utilities manage data for many thousands of customers, systematic data-handling inaccuracies can easily be masked by the shear volume of the bulk data. Figure 11.2 gives an overview of the typical steps existing in the data trail from meter to historical archive. In any of the above steps errors can be introduced into the output...

Iwaawwa Recommended Performance Indicators for Nonrevenue Water and Real Losses

Leakage Management Iwa

During the period 1996 to 2000, various IWA Task Forces undertook a detailed study to determine the most appropriate performance indicators for different water supply purposes. Table 7.4 below shows the PIs for nonrevenue water and real losses recommended by IWA1,2,8 converted to North American units. The PIs are categorized by function and by level, defined as follows Level 1 basic A first layer of indicators that provide a general management overview of the efficiency and effectiveness of the...

The IWA Approach to Calculating Unavoidable Annual Real Losses

The IWA approach is described in detail in the December 1999 issue of the IWA AQUA Magazine,8 and can be seen as a natural development of previous North American attempts to take key local factors into account. The component-based approach is based on auditable assumptions for break frequencies, flow rates, durations background and breaks estimates concepts9 to calculate the components of unavoidable real losses for a system with well-maintained infrastructure speedy good-quality repairs of all...

Real Losses

The quantity of real losses in a given water systems is a good indicator of how efficient a water supplier is in managing its assets the distribution network and the product it delivers to its customers. Volumes of real losses that are significantly higher than what is economically justifiable indicate that action needs to be taken if the water supplier is to be viewed as water-efficient, customer-responsive, and a responsible steward of water resources. Real losses are made up of three...

Modeling the Effects of Changing System Pressure on Leakage Flow Rates and Volumes Using FAVAD

Predicting the Reduction in Break Flow Rates Theoretical hydraulics3 tells us that the equation for fully turbulent flow Q, through a fixed orifice of area A, at static head h follows the square root principle, whereby Qf is proportional to the orifice area Af and the real fluid exit speed V, which varies with the square root of the static pressure h, and a discharge coefficient C However, if the area of the orifice, and or the coefficient of discharge Cd, also changes with pressure, then the...

Component Analysis and Modeling of Apparent Loss

Modeling components of apparent losses has been done in many forms for many years. One example of apparent loss modeling is the attempt to quantify the volume of water not registered due to customer meter underregistration. However, in recent years component analysis of apparent losses has been approached in a similar manner as the methods of real losses modeling where components of apparent loss are shown as multiples of an unavoidable annual volume. In Table 10.5, first attempts at a...

Modeling Background Losses

Background losses are individual events small leaks, weeping joints, and the like with flow rates too low to be detected by visual inspection or traditional acoustic leak detection techniques. They will continue to flow unless either detected by chance or until they gradually worsen to a point where they can be detected. The level of background leakage tends to increase with increasing age of the network and is higher for systems operated at higher pressure. The type of pipe materials and...

Customer Meter Inaccuracy

Customer meters that inaccurately measure the volumes passing through them can be a major source of apparent loss in drinking water systems. While most North American drinking water utilities meter their customer consumption, a notable number do not. For example, only 56 of all residences in Canada were metered as of 1999, therefore many customers are unmetered and typically pay a flat-rate fee for water service.1 In unmetered water utilities, meter accuracy cannot be evaluated as an apparent...

Active Leakage Control

The purpose of active leakage control ALC is to find leaks that do not surface or otherwise come to the attention of the operating company through customer contact, for example, poor supply, loss of water, and so on. These leaks are often referred to as reported leaks. The process of active leakage control involves teams of leakage detection staff sweeping an area to find leaks generally using sounding techniques or similar. This may be in response to an increase in a nightline if the area is...

Topdown Water Audit Spreadsheet Models

The water audit methodology recommended for use in this publication was jointly developed by the International Water Association IWA and the American Water Works Association AWWA and published in 2000. By compiling a water audit using the standardized IWA AWWA methodology, water utility auditors gain an understanding of the nature and extent of their system water loss volumes and, via the validation process, allows the utility to calculate the mathematical confidence in those annual volumes....

Determining Authorized Consumption

Definition The annual volume of metered and or unmetered water taken by registered customers, the water supplier, and others who are authorized to do so. The calculation of the annual billed metered consumption goes hand in hand with the detection of possible billing and data-handling errors, information which is required at a later stage of the water audit process for the estimation of apparent losses. Consumption of the different consumer categories e.g., domestic, commercial, or industrial...

Hiki S. 1981 Relationship Between Leakage Andpressure

Trow. Managing Water leakage economic and technical issues. Financial Times Energy. 1998. ISBN 1 94083 011 5 2. Lambert, A., T. G. Brown, M. Takizawa, et al. A review of performance indicators for real losses from water supply systems. Aqua. 48 6 , December 1999. 3. Thornton, J., Garzon, F., and Lambert, A. Pressure-Leakage Relationships in Urban Water Distribution Systems. International Conference on Water Loss Management. Skopje, Macedonia ADKOM USAID GTZ,...

Customer Meter Demographics and Consumption Record

Water utilities that employ best management practices for meter management usually have a thorough understanding of their customer meter demographics and the accuracy of the different meter types in their system. Many water utilities, however, are not current with the status of their meter population. It is not uncommon for an incoming water utility manager to inherit a meter population that was installed 15, 20, or 25 years ago but hasn't experienced ongoing meter testing, rotation, or...

Loss Of Water Globally

A standardized International Water Association's IWA American Water Works Association AWWA water balance provides the water utility with the necessary results and understanding of the nature and extent of its water losses. Subsequently, the water utility will be able to select the appropriate tools for intervention against real and apparent losses. Just as businesses routinely prepare statements of debits and credits for their customers, and banks provide statements of monies flowing into and...

Modeling Components of Real Losses Using Breaks and Background Estimates Concepts

National Leakage Control Initiative, a systematic approach to modeling components of real losses leakage and overflows was developed by Allan Lambert. Recognizing that the annual volume of real losses is the result of numerous leakage events, each individual volume loss being influenced by flow rate and duration, Lambert considered leakage events in three categories Background undetectable leakage Small flow rate, runs continuously Reported breaks High flow...

Background Leakage and Backlog Removal

Background leakage is generally defined as the leakage below the level of detection with current technology . The level of background leakage can be assessed using a number of methodologies.7 However, the level of background leakage is a function of the extent and method of leakage detection employed, which itself will have different operating costs associated with different levels of leakage. Therefore, a matrix of leakage detection costs versus level of background leakage can be derived, from...

Summary Source Meter Accuracy

Source meters register the bulk water resource supply to the water utility, as well as interconnection transfers between water utilities, major treated water transmission flows into and out of tanks and other storages, and flows across pressure zones and district metered areas. These meters provide the input that goes into the value of water supplied which is the first primary component in the water audit. Appreciable error in source meters and the water supplied value can carry throughout the...

Source Meter Accuracy and Testing Program Steps

Treated drinking water is commonly measured by meters, but untreated source water from lakes, reservoirs, streams may be measured by other devices, such as Parshall flumes or weirs. Any unreasonable degree of error in a measuring device must be discovered and corrected incorrect supply data compromises the water audit since any error in the source meters carries throughout the audit. To be sure that meters are accurate, compare the results of meter tests to applicable AWWA standards and...