Page 334 - Water Loss Control

Contr olling Real Losses—Pr essur e Management 303

a pressure management scheme. When considering reduction of leakage practitioners
usually think of pressure reducing functions, however, in many cases, in particularly
pumped systems, leakage can be reduced greatly by surge anticipation.

Water Conservation
In direct pressure use situations, see Fig. 18.2 pressure reduction can be an effective way
of controlling unwanted demand. A simple example is somebody cleaning their teeth
for 5 minutes at a high pressure or 5 minutes at a low pressure. If the tap is left on for
the duration, much less water will be consumed at the lower pressure.
This is not the case in tank-fed residential situations as in Fig. 18.3 as the head con-
trolling the demand is a function of the height above the equipment being used not the
incoming pressure. (Work is being undertaken by practitioners in areas with residential
tanks to better understand the role that pressure management may play in the reduc-
tion of ball valve leakage, which often goes undetected as meters have trouble reading
these low flows. It has been noted that below certain pressures the ball valves stop leak-
ing with no further intervention needed. This may in effect mean that pressure manage-
ment can also have a positive effect on apparent losses).
While many utilities may not want to reduce demand, because they will have a
negative impact on their billing, many other utilities have found that it is much more
cost-effective to reduce demand than to implement costly capital expansion programs
to increase supply or meet excessive demand peaks. Utilities with direct feed systems
should carefully analyze the demand types within the residences and commercial
industrial customers, as many demands are volumetric and therefore will not be affected
by pressure reduction other than fill time changes.
Nonpayment
Some utilities are faced with a nonpayment situation, which is difficult to resolve due
to political, or social pressure meaning that they have to continue to supply water even
though the customers are not paying. In these situations pressure management to

Mixed volumetric and direct pressure use

House

Affected by pressure
Shower
Not affected by pressure
Toilet
Bath

Meter Garden Sink
hose Washer
Pool
Road

Service
Main
FIGURE 18.2 Residential demand direct feed.