Page 188 - Water Loss Control

162 Cha pte r Ele v e n

Customer Economic level of apparent
meter losses
inaccuracy

Unavoidable
annual apparent Data transfer errors
Unauthorized losses between meters
consumption and archives; poor
Potentially
customer accountability
recoverable apparent
losses
Data analysis
errors between
Current annual apparent losses archived data
and data used
for billing/water
balance

FIGURE 11.3 The four pillar approach to the control of apparent losses. (Source: Ref. 6.)

• The inner box is the level of unavoidable annual apparent losses (UAAL). This
is a conceptual level of apparent losses representing the lowest level that could
be attained if all possible apparent loss controls could be exerted. Unlike the
unavoidable annual real losses (UARL) which has an established calculation,
an established formula or reference value for the UAAL does not currently
exist. Discussion on the means to develop a calculation for the UAAL continues
among the IWA Water Loss Task Force.
• The four arrows represent means to address the four significant causes of
apparent losses. The arrows indicate that, as targeted actions exert control over
certain components of apparent loss, the total annual volume of apparent losses
(outer box) can be reduced. The dual directional structure of the arrows reflect
that lack of control of these component areas results in the total volume of
apparent loss increasing.
Controlling losses in almost any field of endeavor is an effort of diminishing returns,
as many losses can never be completely eliminated. When losses are rampant, relatively
large reductions can often be gained early in a loss-control program; this is the “low
hanging fruit.” However, further loss reduction requires ever-greater cost and effort to
recoup ever-diminishing returns. Figure 11.4 provides an example cost curve for cus-
7
tomer meter replacement, with points plotted at replacement frequency (years) and
average cumulative consumption passed through the meters (million gal). It can be
seen that replacing meters at a high frequency results in less apparent loss due to meter
inaccuracy. However, a high replacement frequency means higher replacement costs.
So, when is the optimum time to replace meters?