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is not fully shut-tight, then the drop in flow will not be correct. Therefore it is necessary
to carefully evaluate if a step-test is the appropriate method to be used. 1

16.5.4 Leak Noise Logger Survey
Leak noise loggers are a relatively new technology compared to other acoustic leak detection
instruments. They have been used in various forms for about the last 15 years. Noise loggers
are installed on pipe fittings such as valves and hydrants through the use of a strong magnet.
They are programmed to listen for noise generated by leaks. Noise loggers typically record at
1 second intervals over a period of 2 hours during the night, when background noise is likely
to be lower. By recording and analyzing the intensity and consistency of noise, each logger
indicates the likely presence (or absence) of a leak. Noise loggers can either be permanently
installed in the distribution network, or temporarily for a user definable period (mostly one or
two nights). Noise loggers only indicate the presence of a leak and do not provide the exact
location of the leak. Therefore, it is necessary to follow up on an indicated leak with a pin-
pointing exercise to exactly determine the location of the leak for excavation and repair.
16.5.5 Leak Noise Mapping
Noise mapping is an improved form of regular acoustic survey pioneered by the Hali-
fax Regional Water Commission. Locations for sounding are predetermined (mainly
hydrants), and the level and type of leak noise (reading taken from the leak detection
equipment) is written down on a map. In addition, the presence or absence of noise is
entered into a spreadsheet with standardized information on date, location, general
description, leakage inspector, and noise sound legend. The next step is to validate the
recorded noise and document the results in the same spreadsheet. This process is only
completed when all recorded noises have been validated. The leakage manager can
now easily control the work of the inspectors and can compare actual noise levels to
previous ones and thus, easily identify areas where more detailed leak detection activi-
ties are needed. This is a simple but very effective improvement of regular sounding
surveys which can best be applied in distribution systems with a very high hydrant
density where the sounding points can be identified easily. 2

16.5.6 Summary of Leak Detection Techniques
Understanding the nature of leakage occurrences in a distribution system and the relative
capabilities of leak detection equipment, techniques and staff training and experience is
1
important to the successful control of leakage levels. Tables 16.1a and 16.1b provide a sum-
mary of specific characteristics of each leak detection technique mentioned above.
Every leak survey needs preparation in order to achieve good results. The practitioner
should consider the following points when planning a survey and evaluating the results.
Presurvey Checklist

• Prepare good system plans at workable scales.
• Clearly mark limits of zone(s) to be tested.
• Locate unknown pipe lengths.
• Identify a suitable distance between testing points per main type.
• Identify large users who could interfere with sounding.
• Identify locations of pressure reducing valves and their inlet/outlet pressure
ranges.