Detecting Leakages

Techniques to reduce NRW

One of the major issues affecting water utilities across the globe is the difference between the amount of water that runs in the distribution system and the actual amount of water that is billed to consumers, also called non-revenue water (NRW). High levels of NRW reflect the fact that large volumes of water are being lost through leaks and not being invoiced to consumers. This adversely affects the financial viability of water utilities in the form of lost revenues and high operational costs. Reducing these water losses is critical to efficient resource utilisation, effective utility management and enhanced customer satisfaction.

In order to address the issue of NRW, several leak detection technologies are being adopted by water utilities to facilitate easier and faster detection of leakages in water distribution pipelines. Utilities in Kerala, Gujarat and Maharashtra have been actively adopting advanced technologies and measures to reduce the NRW component in the total amount of the water supplied.

Current practices for leakage detection and management

One of the first steps in reducing NRW is the constitution of small district metered areas for managing the water distribution network. This helps in accurate measurement of the flow and leakages. The level of NRW is kept to a minimum by analysing the flow data, which makes early detection of leakages possible. Advanced equipment and tools such as sensors, ultrasonic flow meters and bulk meters are installed throughout the distribution network including the transmission mains, reservoirs and distribution mains to detect leakages at all points of the distribution chain.

To deal with leakages from the transmission mains, insertion meters or clamp-on ultrasonic meters are positioned at each end of the mains to calculate changes in the volumetric flow rate and thereby detect leakages. Leakages from water reservoirs are measured through the reservoir drop test, wherein the inlet and outlet valves are closed and the drop in water level is measured over time. If the reservoir has compartments, each of them is monitored individually. Overflowing reservoirs is another major cause of water loss, which usually results from faulty float valves. These valves are thus inspected when the reservoir is at the top water level.

The other key equipment and tools deployed to keep water leakages in check include listening sticks, noise loggers, acoustic sound sensors and noise correlators. Listening sticks comprise two chromium-plated mild steel bars, which transmit leak noise vibrations to a brass diaphragm fitted in a resonant chamber. These vibrations are mechanically amplified to enable the user to listen to and detect any potential leaks. Some of the major advantages of using listening sticks are their low cost, ease of use, high portability and durability. Sound-based leakage detection techniques have been adopted by the Vadodara Municipal Corporation and the Municipal Corporation of Greater Mumbai.

Noise loggers are mainly used to detect leakages in pipelines by analysing the noise resulting from existing leaks. These are generally put to use at night when there is minimum background noise. A major advantage of these noise loggers is that they are capable of detecting leakage noise at a frequency range of 1 MHz to 3000 MHz.

Another way of detecting leakages is to place microphones or acoustic sound sensors in contact with the pipe at two or more points. This helps in recording the sound emitted by a leak. If the distance between the sensors is known in advance, the difference in the time it takes for noise to travel from the leakage site to each of the sensors can help determine the location of the leak.

Recent innovations and technologies

In recent times, several new and advanced technologies have been adopted by water utilities in order to reduce the level of NRW in the total water supplied. Chief among these are internet of things (IoT)-based smart pipes, leak detection robots and SmartBall leak detection technology.

IoT-based smart pipes: IoT-based smart pipes make use of an underground wireless sensor network (UWSN) for leak detection in water pipelines. It is based on force-sensitive resistor technology. In the UWSN, each node communicates with the nodes in front and behind itself via radio frequency signals. For every four to five nodes, there is a master node that has the capability to communicate with the sensor nodes via radio frequency transmission. These master nodes connect to the internet and transmit the received data from the nodes to the cloud. The data in the cloud can then be accessed via different devices with internet connectivity. These wireless smart sensor network systems offer several inherent advantages such as easy installation without jeopardising the pipes’ structural integrity and allow for continuous monitoring without operator intervention. Lastly, ultra-low power smart wireless sensor networks allow them to stay operational for extended periods of time without maintenance, thereby making them viable for both the existing and new power supplies.

Leak detection robots: In-pipe leak detection robots use pressure gradients to identify leaks. The detector, which operates autonomously, can sense leaks at any angle around the circumference of the pipe with only two sensors. Though this technology is still at the research stage, it has already been demonstrated in the US and Saudi Arabia. A major advantage of this technology is that it works regardless of the size or material of the pipe. Further, it remains relatively insensitive to the fluid medium inside the pipes, thereby making this detection method widely applicable. Lastly, the pipes do not have to be drained for installing this technology and hence, service remains uninterrupted. This technology, developed by the Massachusetts-based Mechatronics Research Laboratory, is expected to be made available in the market within two years.

SmartBall leak detection: The SmartBall leak detection technology makes use of an advanced tool to identify leakages and air pockets in water supply pipelines. In this, a ball-shaped, free-swimming device with a diameter of 150 mm is used. It is equipped with a sensitive acoustic sensor, which is capable of locating very small leaks, with water leakages as low as 0.028 gallon per minute. It can identify these leakage points within 6 feet of their actual location.

To conduct inspections, the SmartBall tool is inserted into a pipeline that is at least 350 mm in diameter. It is equipped to travel with the water flow in the pipeline for up to 16-18 hours per deployment. Therefore, it can complete long surveys in a single deployment, without causing any disruption to regular pipeline services.

Two access points need to be identified along the pipeline for deploying this sensor, one for the insertion of the SmartBall and the other for its extraction. The tool can be tracked throughout the inspection process by installing GPS or sensor meters at predetermined locations on the pipeline. This helps in getting real-time data about the location of the SmartBall and the portions of the pipeline that are affected by leakages and gas pockets. In India, the SmartBall leak detection technology has been adopted by the Kerala Water Authority.

Issues and challenges

One of the major challenges in the reduction of NRW is the lack of standard norms for defining and quantifying its components. In the developing countries, only a small percentage of the water utilities establish a water balance. Even if they do so, no standard approach or terminology is used and hence, they end up being different from each other. As a first step, all water utilities need to undertake asset mapping and prepare a baseline for establishing the current levels of water losses. This can be accomplished by carrying out a water audit for establishing the water balance, which is a prerequisite for designing a NRW reduction strategy.

Many water utilities in Asia practise passive leakage control, meaning that they repair only those leaks that are visible. This is clearly not enough since 90 per cent of the leaks are usually not visible on the surface. This means it takes far too long, often many years, before the utility is even aware that there is a leak. Since awareness time largely determines the volume of the water lost from a pipe burst, utilities need a strategy to reduce the awareness time.

Commercial losses are nearly always less in volume than physical losses, but this does not mean that commercial loss reduction is any less important. In fact, commercial loss reduction has the shortest possible payback time, as any action immediately results in an increase in billed volumes and revenues. In order to reduce commercial losses, customer meter management should be undertaken holistically, wherein utilities should seek to select the appropriate meter type and prepare tailored specifications. To address billing issues, there is a need to design billing systems in a manner that retains the integrity of the consumption data. Further, a stringent inactive account management and verification programme can help in the identification of connections where the contract has been terminated but the tapping point on the main still exists, and can be easily reconnected illegally.

Conclusion

Globally, the NRW problems faced by water utilities are substantial and, therefore, immediate steps are needed to address them. Water utilities need to adopt an appropriate design for system expansion and use higher quality materials and equipment. In addition, regulators and policymakers should require water utilities to undertake periodic water audits and regularly publish detailed NRW data, which can then be independently audited. Although an intensive and comprehensive programme is required to reduce NRW, sustainably low levels of NRW can only be achieved if NRW management becomes a part of the normal day-to-day activities of water utilities. n

Based on a presentation by Dheeraj Kaushik, Senior General Manager, Tata Consulting Engineers, at a recent India Infrastructure conference

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