The most effective way to find leaks in underground water pipes is with acoustic water leak detection equipment. This technology is based on the principal that as water escapes through the leak a mechanical vibration is generated and this vibration is audible with acoustic water leak detection equipment. When there is no pressure in the pipe because it is partially full or there is a complete rupture, a mechanical vibration is not generated and the leak cannot be detected acoustically. Different acoustic water leak detection equipment is used in the three stages of active leakage control designed for water distribution networks by the International waterloss taskforce, localisation, location and pinpointing.
If the water network is managed in districts and minimum night flow data is monitored to identify rises in leakage the leak positions can be localised with step testing, listening to each service connection with a listening stick or using leak noise loggers. Because step testing and listening stick surveys are labour intensive and often require night work, leak noise loggers are usually the favoured option. It is not necessary to have the network sectioned into manageable districts to commence an active leak detection program however this minimum night flow data helps with the prioritisation of resources, understand the rate of rise (leakage) and performance of the network.
When the leak position has been localised to section of pipe about 100 meters long (or less), leak noise correlators are used to locate the leak position. Transmitting acoustic sensors are deployed on valves, hydrants or exposed sections of the pipe either side of the leak position, pipe information between these two points is entered into the correlator and a peak is created on the correlation screen showing the point with the loudest noise. If the leak is not the loudest noise, filters may enable the operator to reveal the leak position. The leak location provided by a correlator is often accurate to within 1 metre (or less) but if incorrect pipe information has been entered this error will be greater. The operator is often unaware about changes in materials or mixed materials for pipe repairs, so it is important to the pinpoint the leak with an acoustic microphone.
The path of the pipe should be marked on the ground and acoustic microphones are used to pinpoint the leak by identifying the point with the highest acoustic signal. On bitumen surfaces the operator can use a ground microphone or pocket microphone by placing them on the ground or they can drill or punch holes in the ground and insert a listening stick. On concrete slab the tripod foot or listening stick usually provide the best response, as a ground microphone is too sensitive. On grass or dirt the operator will get best results with the listening stick and punching holes with a T probe or plunger bar. If the ground is soft and water logged around the leak, the noise may actually be louder either side of the leak because the noise travels better through the compacted dry ground.
The same principles of leak localisation, locate and pinpoint apply with leak detection in houses and the same acoustic water leak detection equipment is used. However the process is a little different. The Aquascope 3 acoustic water leak detection equipment and a pipe locator is generally all that is required unless there are very long sections of pipe when an Aquascan 610 leak correlator will speed up the leak location process. Use the electronic listening stick in the Aquascope 3 acoustic water leak detection kit to localise the leak position. Use a pipe locator to locate the path of the pipe and then use the Aquascope 3 to pinpoint the leak. There are three different acoustic microphones in the Aquascope 3 acoustic water leak detection equipment kit. For underground leaks in soft ground insert several probes and listen with the listening stick to pinpoint the position. Under concrete slab use the pocket mic or tripod foot to pinpoint the leak. Under a sealed surface use the ground microphone.