Page 98 - Water Loss Control

80 Cha pte r Se v e n

7.4.1 Determining the System Input Volume

Defi nition: 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 por-
table flow-measuring devices, or if possible by conducting volumetric comparisons via
reservoir drop test, for example. If any inaccuracies of the system input meters are
revealed it is necessary to further investigate the problem, and if necessary, the recorded
volume of water has to be adjusted to account for the inaccuracy of the system input
meter. It is recommended that as well as verifying the accuracy of the meters, the entire
data recording chain from the raw 4 to 20 mA signal produced by the meter to the
Supervisory Control and Data Acquisition (SCADA) archive is checked when testing
the input meters.
If there are unmetered sources then the annual flow has to be estimated by using
any (or a combination) of the following:

• Temporary flow measurements using portable devices
• Reservoir drop tests
• Analysis of pump curves, pressures, and average pumping hours

It is important to realize that the accuracy and reliability of the water balance results
are directly linked to the accuracy of the figures used for the system input volumes. It
is recommended that system input meters are tested for their accuracy at least once a
year so they can be recalibrated if necessary.

7.4.2 Determining Authorized Consumption

Defi nition: The annual volume of metered and/or unmetered water taken by registered customers, the
water supplier, and others who are authorized to do so.

Billed Metered Consumption
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. Consump-
tion of the different consumer categories (e.g., domestic, commercial, or industrial)
have to be extracted from utility’s billing system analyzed and validated. Special atten-
tion should be given to the group of very large consumers.
The annual billed metered consumption information taken from the billing system
has to be processed for meter reading time lag to ensure that the billed metered con-
sumption period used in the audit is consistent with the audit period.

Billed Unmetered Consumption
Billed unmetered consumption can be obtained from the utility’s billing system. In
order to analyze the accuracy of the estimates, unmetered domestic customers should
be identified and monitored for a certain period, either by the installation of meters on