Page 72 - Water Loss Control

54 Cha pte r F i v e

In 1994, a concept called Burst and Background Estimates (BABE) was published,
acknowledging that the annual volume of real losses consists of numerous leakage
events, where each individual loss volume is influenced by flow rate and duration of
leak run time before it is repaired. A component-based leakage analysis breaks leakage
down into three categories:
• Background leakage (undetectable): Small flow rate, continuously running
• Reported breaks: high flow rate, relatively short duration
• Unreported breaks: moderate flow rates, the run time depends on the intervention
policy
It is not recommended that a component analysis is undertaken on its own to derive
a volume of annual real losses because there is likely to be a significant level of uncer-
tainty in much of the data used in the analysis. However, a component analysis is a very
useful supplement to a top-down water balance because it provides estimates of the
volumes of real losses in different elements of the distribution infrastructure. This data
is so valuable because it is required to develop the most appropriate loss reduction strat-
egy and it is essential for a robust determination of the economic level of leakage (ELL).
As depicted in Fig. 5.1 the water balance calculates the total volume of real losses for
the audit year. However, it does not provide the information on what portion of these
real losses is due to hidden losses (losses from leaks that have not been captured by the
utilities current leakage management policy). By assessing the volume of real losses
through component-based analysis, it is possible to determine the volume of real losses
that have been captured through the current leakage control policy. Therefore, by
deducting the real losses based on the component-based analysis from the real losses
based on the top-down water balance, it is possible to determine the volume of hidden
losses.

Hidden losses = real losses from top-down water balance
− real losses from component analysis
The results from this analysis can then be cross checked against the real loss vol-
umes measured in DMAs (see Sec. 5.2.3).
Water balances and component analysis of real losses have to be carried out at least
once a year since they are such an integral part of any water loss control program. Many
utilities establish water balances on a monthly basis to keep a close eye on their water
loss management performance.

5.2.3 Bottom-Up Analysis of Real Losses Using DMA and
Minimum Night-Time Flow Analysis
The two ways of assessing real losses explained in the previous sections can be general-
ized as desktop analysis. However, an MNF analysis uses field test data to quantify the
volume of real losses within the distribution network. The results can be directly com-
pared with the volume of real losses obtained from the top-down water balance. A
DMA is required in order to conduct MNF measurements. A DMA is a hydraulically
discrete part of the distribution network that is isolated from the rest of the distribution
system. It is normally supplied through a single metered line so that the total inflow to
the area is measured (Fig. 5.2).