Page 338 - Water Loss Control

Contr olling Real Losses—Pr essur e Management 307

Loss of Revenue
As far as the loss of revenue is concerned, systems with high leakage will almost always
see a positive benefit from pressure management, even when stacked against a poten-
tial loss of revenue, due to reduction of pressure in the residence or industry.
Any lost revenue is included in the cost to benefit calculations as a cost against the
project just as installation and product costs are included.
This is also true for systems with lower losses and high costs to produce or purchase
water. In situations where a loss of revenue cannot be tolerated, pressure management
can be limited to nighttime hours, when legitimate consumption is at its lowest and
system pressures are at their highest.
Remember also that many systems are enforcing water conservation programs.
Pressure reduction, is also a water conservation program.
A large portion of water use within a household is from the toilet; tank type toilets
use a fixed volume, which does not change significantly when pressure is reduced.
There are, also many other fixed volume uses within
a residence, which will not vary significantly with
pressure, see Fig. 18.2 previous.
For a detailed breakdown
When considering pressure management for a of usage in the United States
sector, we must consider the per capita use and if
the AWWA has recently under-
this is excessive. Sample per capita uses can be
found in Table 18.1. taken an excellent residential
If it is excessive then pressure management will end use study, which can be
become a natural part of a conservation program. If purchased through the AWWA
it is not, we must decide on the components of con- web site.
sumption within the sector (residential, commercial,
industrial), the volumetric consumption and the consumption directly tied to pressure.
We can then analyze the potential benefits of loss reduction over reduction in revenue.

Reservoir Filling
Regarding reservoirs not filling at night because of reduced system pressure, many
pressure reduction programs concentrate on the smaller mains, therefore allowing
reduction of losses in selected areas, while allowing normal system pressure in the
larger trunk or transmission lines. (As with the example in Fig. 18.4, a complete pres-
sure management project can in some cases actually improve reservoir-filling charac-
teristics). This is particularly important in pumped systems where the storage tanks
balance on the system pressure. Gravity systems are less affected.
Reservoirs are usually connected with the larger pipes, so there should not, in many
cases be a problem. Most utilities find that nonvisible leakage tends to be on the smaller
pipes and service connections, so the effectiveness of a potential pressure management
program should not be reduced significantly, by the exclusion of larger pipes in the
control area. See Fig. 18.6.

18.3 Various Types of Pressure Management
Pressure management comes in various forms from the basic sectorization of a gravity sys-
tem to dynamically controlled automatic control valves (ACVs) or pump speeds. Every dis-
tribution system in the world may have different requirements or indeed multiple