WMI - Water Management International
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This glossary includes some technical terms related to our areas of expertise.
Acoustic logger
An electronic device to record levels of noise created by a leak at predetermined time intervals. May be used to detect leaks by accoustic correlation.
Active Leakage Control (ALC)
The process by which unreported leaks are detected and repaired. This contrasts with Passive Leakage Control.
Apparent Losses or Commercial Losses
Apparent losses, which are also called commercial losses, include 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).
Average Zone Night Pressure (AZNP)
The property-weighted average pressure in a zone during the minimum night flow period.
Billed Authorized Consumption or Revenue Water
Authorized Consumption which are billed and generate revenue (also known as Revenue Water). It is equal to Billed Metered Consumption plus Billed Unmetered Consumption.
Billed Metered Consumption
All metered consumption which is also billed.
Billed Unmetered Consumption
All billed consumption which is calculated based on estimates or norms but not metered.
Current Annual Real Losses (CARL)
They are obtained by deducting the water volume related to the theft of water and the volume resulting of domestic underestimation of consumption.
Customer Night Use
Water used by customers during the minimum night flow period. It is usually mesured between 2 a.m. and 3 a.m.
District Metered Area
Small discrete metered area within the distribution network. The term Distribution monitoring Area is also used to describe the same.
DMA's Establishment
To manage large distribution networks efficiently, especially those with poor infrastructures, it is necessary to break them down into network zones and subzones (District Metered Areas - DMAs). This helps to obtain a comprehensive understanding of the water consumption and water loss within the various parts of the network.
Geographic Information System
Ground Microphone
Device placed on the groundlevel which amplifies the sound created by a leak to facilitate its location.
ILI (Infrastructure Leakage Index)
The ILI is representative of how well a distribution network is managed (maintained, repaired, rehabilitated) for the control of real losses, at the current operating pressure. It is the ratio of current annual volume of real losses (CARL) to unavoidable annual real losses (UARL). ILI = CARL/UARL.
Escape of water through any aperture as for example a hole, a crack or a fissure.
Leak Noise Correlator
An electronic device for matching the sound frequency spectrum from two different locations for the purpose of locating or pinpointing leaks.
Losses are made up of Apparent Losses (meter errors and unauthorized consumption) and Real Losses. Real Losses are equivalent to leakage.
Meter Management
Meter testing, maintenance and replacement in order to ensure that meter underregistration will be kept to a minimum and consequently the water utility's revenues will be optimised.
Minimum Night Flow (MNF)
Net flow into a metered area during the period of minimum flow: this period is usually one hour between 2 am and 3 am.
Non-Revenue Water (NRW)
NRW is the difference between the total system input volume and billed authorized consumption, and it consists of the following:
  • Unbilled Authorized Consumption (usually a minor component of water balance),
  • Apparent Losses, and
  • Real Losses.
Output-Based Management
Improvement of management effectiveness and accountability by defining relevant expected results, controlling progress through the achievement of expected results, incorporating lessons learned into management decisions and reporting on performance.
Passive Leakage Control
Repairing only those leaks that become visible and are reported to the Water Utility.
Performance-Based Contract
Contractual agreement defined on what has to be achieved and not necessarily how it has to be done. Fixed remuneration and success incentive are usually established between the parties.
Real Losses
Volume of water lost through all types of leaks, breaks and overflows on mains, service reservoirs and service connections, up to the point of users metering.
Revenue Water
Authorized Consumption which are billed and generate revenue (also known as Revenue Water). It is equal to Billed Metered Consumption plus Billed Unmetered Consumption.
Step Test
The purpose of a measure by "Step Test" is to know the distribution of Night Flows. Analysis of these flow make possible to quantify the physical losses and to establish priorities for leaks action on a limited area.
System Input Volume
Annual volume of treated water put into the water supply system that relates to water balance calculation.
Unauthorized Consumption
All unauthorized use of water as for example illegal connections, illegal water withdrawal from hydrants (for example for construction purposes), bypasses to consumption meters or meter tampering.
Unavoidable Average Real Losses (UARL)
Theoretical reference value representing the technical low limit of leakage that could be achieved if all of today's best technology could be successfully applied. This is a key variable in the calculation of the Infrastructure Leakage Index (ILI).
Unbilled Authorized Consumption
The Authorized Consumption which is legitimate but not billed and therefore do not generate revenue. It is equal to Unbilled Metered Consumption plus Unbilled Unmetered Consumption.
Unbilled Metered Consumption
Metered Consumption which is unbilled whatever the reason. This might include water provided to institutions free of charge or metered consumption by the utility itself.
Unbilled Unmetered Consumption
All Authorized Consumption which is neither billed nor metered. This component includes items such as flushing of mains and sewers, street cleaning, fire fighting, frost protection, etc.
Water Loss
It is the difference between Total System Input and Authorized Consumption. Water Losses are made up of Physical Losses and Commercial Losses.
Water Utility
General term to designate the organization responsible for operation of the water supply and distribution system.
Zero Pressure Test
It is used to establish if an isolated section of the supply network , often referred to as a DMA, is indeed isolated. The methodology is to establish an area that can be isolated by closing supply and boundary valves. This is done by examining a supply network map.