Page 99 - Water Loss Control

Evaluating W ater Losses 81

those non-metered connections or by monitoring a small area with a number of unme-
tered customers. The latter has the advantage that the customers are not aware that they
are metered and so they will not change their consumption habits. In the unlikely case
that nondomestic customers are unmetered, detailed surveys have to be carried out to
check the accuracy of the estimated billed consumption figures.
Unbilled Metered Consumption
The volume of unbilled metered consumption has to be established similar to that of
billed metered consumption.

Unbilled Unmetered Consumption
Each type of unbilled unmetered consumption shall be identified and individually esti-
mated by building up from individual usage events using a component-based approach
to develop a realistic estimate of use, for example:
• Street cleaning/sewer flushing: Components to be assessed are what is the number
of street cleaning trucks in operation? What is the volume of water a street
cleaning truck transports? How many times is a street cleaning truck filled per
month? The street cleaning and sewer flushing departments should be able to
provide the necessary data.
• Mains flushing: How many times per month? For how long? How much water?
The operations and construction departments should be able to provide the
necessary data.
• Fire fighting: Number of fires during year? Average volume per fire? Has there
been a big fire? How much water was used? The fire department should be able
to provide this data.
• Fire flow tests: How many tests in year? Average duration of test? Flow rate?
Again the fire department should be able to provide this data.
In some circumstances, it may be appropriate to meter a small sample of these use
events to obtain a better estimate of use per event.
7.4.3 Calculation of Water Losses

Defi nition: The difference between system input volume and authorized consumption, consisting of
apparent losses plus real losses.
Water Losses are calculated by subtracting the total authorized consumption volume
from the system input volume. In the subsequent process of the water audit, the volume
of water losses is further broken down into real and apparent losses.

7.4.4 Assessment of Apparent Losses
Defi nition: This component includes unauthorized consumption, all types of customer metering
inaccuracies and data-handling errors.
Unauthorized Consumption
It is difficult to provide general guidelines of how to estimate unauthorized consump-
tion. 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