Page 42 - Water Loss Control

24 Cha pte r T h ree

during the 1990s has been the large amount of water loss occurring on the customer
service piping branching from the water main and supplying water to a single or mul-
tiple user premises. For many systems, leaks on these small-diameter pipes represent
the greatest number of leaks encountered in water
supply operations especially in systems with a high
service connection density. Often supplier policies
Service leaks often cause the
require the customers to own their service lines and
largest volumes of real loss.
execute repairs or replacement when necessary.
Unfortunately, many customers are often unaware
of their ownership responsibilities and, when advised to repair known leaks, are nei-
ther timely nor effective in getting relatively expensive repairs executed. Consequently,
customer service piping leaks can run for considerably long periods, even after being
reported, and account for substantial water loss. Severe drought in England in the mid-
1990s resulted in emergency regulations that required some water suppliers to imple-
ment repairs on leaking customer service lines. The resulting savings in lost water was
found to be so effective and the repair methods so efficient that national regulations
were soon established requiring all water companies to implement policies for company-
executed customer service line leak repairs. Two other notable aspects of this: the cus-
tomers still retained ownership of the lines and, once high initial backlogs of customer
leaks were repaired, the rate of occurrence of new leaks was sufficiently slow that the
repair policies for the water companies were found to be manageable and cost-effective.
This experience demonstrates dramatically the principle that leakage losses are depen-
dent on two primary variables: rate of flow and time permitted to run. Both parameters
must be considered in developing leakage-management strategy. Too often water sup-
pliers lose track of small volume leaks, allowing indefinite leak time to occur and losses
to mount.

What Else Influences the Volumes of Water Lost through Leaks and Breaks
Another tenet employed in recent times by progressive leakage management programs
around the world is the science of pressure management. In designing water infra-
structure engineers have frequently specified distribution system pressure levels with
the primary objective of providing service above a minimum design pressure. How-
ever, local guidelines for providing fire flows, expansion capacity, and safety factors
have frequently resulted in systems supplying water pressures far above minimum
requirements, without consideration for the impact of the excessive pressure. By the
late 1990s, fundamental relationships between pressure and leakage rates were estab-
lished and show that certain types of leaks are highly sensitive to changes in pressure.
It can now be taken that, while certain minimal levels of pressure need to be provided,
maximal levels for pressure should also be estab-
lished and not exceeded. Excessive water pressure
not only increases certain types of leakage, but also
Pressure has a much greater
influences main break rates and the amount of
impact on leakage than origi-
needless energy costs a supplier expends. In pro-
nally suspected. System design
gressively managed water systems, water pressure
should take into account maxi- is now controlled within an appropriate range that
mum pressure limits as well meets the needs of the customer and the supplier
as minimum ones. without causing waste or harmful impact to the
infrastructure.