Non-Revenue Water

Here is another article on this subject.

1.1 General

Why is Non-Revenue Water (NRW) assessment so important for any water utility? It is common knowledge that the NRW in any water utility is a percentage of the water volume pumped into the network - but this simple percentage figure just isn’t sufficient to understand the water utility’ problem and elaborate an appropriate reduction strategy.

Therefore it was necessary to apply the nowadays available methods and tools which had helped to establish a first baseline. The following pages provide a brief overview on the methodology and the related terminology.

1.2 Methodology

Twenty years ago, leakage management was more based on a process of 'guesstimation' than on precise science. This has changed dramatically, kick-started by the regulatory pressure on UK water companies to cut leakage. Significant advances have been made in the understanding and modeling of water loss components and on defining the economic level of leakage for individual system. Yet, despite some encouraging success stories, most water supply systems worldwide continue to have high levels of water losses, many of which are almost certainly higher than their economic level.

Part of the problem was the lack of a meaningful standard approach to benchmarking and

reporting of leakage management performance. Surprisingly few countries have a national standard terminology and standard water balance calculation …and even then, they all differ from each other! Being aware of the problem of different water balance formats, methods and leakage performance indicators, the International Water Association (IWA) has developed a standard international water balance structure and terminology.

This standard format has meanwhile been adopted (with or without modifications) by national associations in a number of countries (for example Canada, Germany, Australia, New Zealand and South Africa and most recently the American Water Works Association (AWWA). This standard methodology is described in this paper which also includes a number of important

1.2.1 The Standard Water Balance

The level of water losses can be determined by conducting a Water Audit (North American Term) with the results shown in a Water Balance (International Term). To be consistent with the new international terminology, the term Water Balance has been used in this report.

A Water Balance is based on measurements or estimations of water produced, imported,

exported, used and lost. Whilst most water utilities are able to provide estimates of water

produced, imported, exported and consumed, they are less able to quantify the different

components of water lost. Water utilities around the world have always established water balances in one or the other way. But unfortunately, a wide diversity of formats and definitions is used, often within the same country. So it was (and still is) virtually impossible to compare UfW, NRW, leakage or water losses of different utilities.

Being aware of the problem of different water balance formats and methods, the IWA has

developed a standard international water balance structure and terminology, as already mentioned above. This form was generated drawing on the best practice of water utilities from many countries.

1.2.2 Water Balance Definitions

In the following, all terms used in Figure 1 above are listed in hierarchical order – as one would read the water balance form from left to right. Some of the terms are self-explanatory but are still listed and briefly explained in order to having a complete list available.

System Input Volume

The volume of treated water input to that part of the water supply system to which the water balance calculation relates – either from own production facilities or bulk supplies from others. If problems with production meters are know, relevant corrections will be made to the System Input Volume.

Authorized Consumption

The volume of metered and/or unmetered water taken by registered customers, the water supplier and others who are implicitly or explicitly authorized to do so by the water supplier, for residential, commercial and industrial purposes. It also includes water exported across operational boundaries. Authorized consumption may include items such as fire fighting and training, flushing of mains and sewers, street cleaning, watering of municipal gardens, public fountains, frost protection, building water, etc. These may be billed or unbilled, metered or unmetered.

Water Losses

The difference between System Input and Authorized Consumption. Water losses can be

considered as a total volume for the whole system, or for partial systems such as transmission or distribution schemes, or individual zones. Water Losses consist of Real Losses and Apparent Losses.

Billed Authorized Consumption

Those components of Authorized Consumption which are billed and produce revenue (also known as Revenue Water). Equal to Billed Metered Consumption plus Billed Unmetered Consumption.

Unbilled Authorized Consumption

Those components of Authorized Consumption which are legitimate but not billed and therefore do not produce revenue. Equal to Unbilled Metered Consumption plus Unbilled Unmetered Consumption.

Apparent Losses

Includes all types of inaccuracies associated with customer metering as well as data handling errors (meter reading and billing), plus unauthorized consumption (theft or illegal use).

Note: Over-registration of customer meters, leads to under-estimation of Real Losses. Under-registration of customer meters, leads to over-estimation of Real Losses.

Real Losses

Physical water losses from the pressurized system and the utility’s storage tanks, up to the point of customer use. In metered systems this is the customer meter, in unmetered situations this is the first point of use (stop tap/tap) within the property. The annual volume lost through all types of leaks, bursts and overflows depends on frequencies,

flow rates, and average duration of individual leaks, bursts and overflows.

Note: Although physical losses, after the point of customer use, are excluded from the

assessment of Real Losses, this does not necessarily mean that they are not significant or

worthy of attention for demand management purpose.

Billed Metered Consumption

All metered consumption which is also billed. This includes all groups of customers such as domestic, commercial, industrial or institutional and also includes water transferred across operational boundaries (water exported) which is metered and billed.

Billed Unmetered Consumption

All billed consumption which is calculated based on estimates or norms but is not metered. This might be a very small component in fully metered systems (for example billing based on estimates for the period a customer meter is out of order) but can be the key consumption component in systems without universal metering. This component might also include water transferred across operational boundaries (water exported) which is unmetered but billed.

Unbilled Metered Consumption

Metered Consumption which is for any reason unbilled. This might for example include metered consumption by the utility itself or water provided to institutions free of charge, including water transferred across operational boundaries (water exported) which is metered but unbilled.

Unbilled Unmetered Consumption

Any kind of Authorized Consumption which is neither billed nor metered. This component typically includes items such as fire fighting, flushing of mains and sewers, street cleaning, frost protection, etc. In a well run utility it is a small component which is very often substantially overestimated. Theoretically this might also include water transferred across operational boundaries (water exported) which is unmetered and unbilled – although this is an unlikely case.

Unauthorized Consumption

Any unauthorized use of water. This may include illegal water withdrawal from hydrants (for example for construction purposes), illegal connections, bypasses to consumption meters or meter tampering.

Customer Metering Inaccuracies and Data Handling Errors

Apparent water losses caused by customer meter inaccuracies and data handling errors in the meter reading and billing system.

Leakage on Transmission and/or Distribution Mains

Water lost from leaks and bursts on transmission and distribution pipelines. These might either be small leaks which are still unreported (e.g. leaking joints) or large bursts which were reported and repaired but did leak for a certain period before that.

Leakage and Overflows at Utility’s Storage Tanks

Water lost from leaking storage tank structures or overflows of such tanks caused by e.g.

operational or technical problems.

Leakage on Service Connections up to point of Customer Metering

Water lost from leaks on service connections from (and including) the tapping point until the point of customer use. In metered systems this is the customer meter, in unmetered situations this is the first point of use (stop tap/tap) within the property. Leakage on service connections might be reported bursts but will predominately be small leaks which do not surface and which run for long periods (often years).

Revenue Water

Those components of Authorized Consumption which are billed and produce revenue (also known as Billed Authorized Consumption). Equal to Billed Metered Consumption plus Billed Unmetered Consumption.

Non-Revenue Water

Those components of System Input which are not billed and do not produce revenue. Equal to Unbilled Authorized Consumption plus Real and Apparent Water Losses.

(Unaccounted-for Water)

Because of the widely varying interpretations and definitions of the term ‘Unaccounted for Water’, the IWA strongly recommends not to use this term any more – an if it is used at least to be defined like Non-Revenue Water. *

Nguyen Cong Thanh - SEAWUN Specialist