Page 307 - Water Loss Control

276 Cha pte r S i x tee n

FIGURE 16.13 Visible leakage from an air valve.

only used for pinpointing a leak. It is a time-saving leak detection methodology which
has one shortfall. Service connection leaks often go undetected in this mode, especially if
the area mainly consists of nonmetallic mains and service connections.
Comprehensive Survey
This survey method listens to all available fittings on the mains and service connec-
tions. Geophones are used to sound above the mains in case contact points are far apart.
Once a leak sound is detected, geophones and leak noise correlators can be used for
pinpointing the leak. Even though this leak detection method is time consuming it is
the most effective way to detect all detectable leaks in the system, including service con-
nection leaks.

16.5.3 Step Testing
Step testing involves isolating sections of the water distribution system into small zones
and measuring the supply to the zone. This is often done on a temporary basis and por-
table flowmeters are used to measure flow into the zone. Every time a section with a leak
is isolated, a marked drop will be seen on the flow graph as shown in Fig. 16.14. This drop
represents the leak volume, which represents valuable information for cost-benefit calcu-
lations and program tracking, and also saves time by directing leak pinpointing crews
only to those sections of the water main where leakage has been proven to be occurring.