Page 71 - Water Loss Control

Steps and Components of a W ater Loss Contr ol Pr ogram 53

5.2.1 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 of
water in the cycle of delivery. The water balance tracks the flow of water from the site
of withdrawal or treatment, through the water distribution system up to the point of
customer consumption. The water balance usually exists in the form of a worksheet or
spreadsheet that details the variety of consumption and losses that exist in a water sys-
tem. The water balance itself is a summary of all the components of consumption and
losses in a standardized format. Every unit of water supplied into the system needs to
be assessed and assigned to the appropriate component. It is certainly not best practice
to have units that are unaccounted for.
It is quite common that the calculated volumes of real and apparent losses have a
relatively low level of confidence the first time a water balance was established. There
are many reasons for a low level of confidence in the calculated water loss volumes the
first time a standardized water balance is established however the most common ones
are that some of the water balance components are not metered and/or the data used
has not been validated. Therefore, it might be necessary to first increase the confidence
in the calculated water loss figures by validating all the volumes entered in the water
balance through meter accuracy testing, improvement of record keeping, and estima-
tion practices and if necessary installing new system input and/or export meters. The
water utility will realize that the auditing process is a revealing undertaking that pro-
vides great insight to the auditor on the type and volumes of water loss (real and appar-
ent losses) occurring in the utility.
The real loss volume calculated through the water balance includes real losses from
leaks that have been repaired (through an active or reactive leakage management pol-
icy), the volume of background losses, and real losses that are due to leaks still running
in the system. The losses caused by leaks which still need to be detected and repaired
by the utility are called hidden losses. However, just by establishing the water balance it
is not possible to estimate the volume of hidden losses. It is recommended as best prac-
tice by the International Water Association (IWA) and American Water Works Associa-
tion Water Loss Control Committee (AWWA WLCC) that the assessment of real losses
using a “top-down” water balance should be complemented by the following two
methodologies:
• Component analysis of real losses: A technique which models leakage volumes
based upon the nature of leak occurrences and durations (see Chap. 10 for more
details)
• “Bottom-up” analysis of real losses: Using district metered area (DMA) and
minimum night-time flow (MNF) analysis (see Chap. 16 for more details)

5.2.2 Component Analysis of Real Losses
As already mentioned, it is best practice that in parallel to establishing a water balance
a component analysis of real losses is carried out to assess the volume of hidden losses
and to get a detailed understanding of the efficiency of the current leak repair policy.