Water features a vital role within the country‘s economic development. It is scarce and needs to be conserved. A considerable amount of water which flows in the water distribution system was found to be lost due to pipe leaks. Leakage is not just an economical issue but it is also an environmental, sustainability and potentially a health and safety issue. Decreasing the amount of non-revenue water due to leakages can play a significant role in saving of the water and increasing the income. Prevention of water wasting in several stages of transmission, refinement and distribution of water is a major aspect of long term water planning.
Introduction to Leakages in Water Distribution Systems
A water distribution system should supply necessary amount of potable water at demand points for domestic, commercial, industrial and firefighting purposes; the system should be capable of meeting the stress almost any time at required pressures. However, sometimes considerable water leakages from the system may cause problems associated with the pressures at the consumers tap and significant water losses. Leakage is defined as the amount of water which escapes from the pipe network by means other than through a controlled action. Water leakage in distribution systems is typically classified into background and burst related leakage. Bursts (i.e. main breaks) represent structural pipe failures and background leaks represent the water escaping through inadequate joints, cracks, etc. Leaks can also exist in service reservoirs and tanks.
The unaccounted flow of water and leakage within the water supply system and the urban water distribution network are paid attention in many countries. Leakage occurs in all water distribution systems nowadays. Scientific and systematic planning of the water distribution system can help to reduce the leakages. Initially the factors causing leakages should be identified and subsequently the leakage management methods can be adopted.
Factors causing the leaks
Leakages in distribution systems can be caused by a number of different factors.
Materials of Pipe : One of the most significant factors causing the leakage in the system is the material of the pipes. It was observed that among various materials of pipes, iron pipes have the most leakage mishaps and asbestos pipes have the least.
Diameter of pipes : The diameter of the pipes is one of the effective element within the rate of the accidents and the losses. The more diameter of the pipe results in thicker the shell of the pipe therefore, the resistance of the pipe increases against the surface or inside pressure .
Pressure in pipes : Another parameter, which decides the performance condition and the overhauling of urban water supply system, is pressure. High pressure in pipes increases the chance of leaks and loss of consumer water. Then again, low pressure in the system causes the failure to provide water or results in giving unsatisfactory water. With high pressure, the performance and suitable servicing of the network is endangered. Changing of the pressure with the prescribed standards is appropriate for a network user.
Age of pipes : The age of pipes features a direct or indirect effect on the quantity of leakage. The studies reveal that with the increasing of the pipes age, the loss can reach to 50% of the entered water into the networks.
Movement of soil around the pipe : The development of the dirt may happen in light of sliding of the ground or shaking of the tremor. This development expedites a great deal of pressure on the pipes and can cause splits in the pipes, holes in the joints or the breaking of the pipes.
Corrosion : The corrosion of the environmental soil and water for all of the metal structures is inevitable (especially about the buried pipes and joints). This corrosion within the motor pumps pipes and taps can happen through cavitation or chemical corrosion of the water system. Pipes may corrode by water from inside and solids from outside due to unsuitable components and salts in water and soil.
Incorrect installation : Installation by unprofessional workers or using incorrect and non-standardized techniques may result in incomplete sealing of the joints. In this case there are some leaks within the joints from the start and it increases over time.
Water Hammer Hit : At the point when water is siphoned into the water supply system a water hammer hit may cause mishaps and break the pipes and joints. Any place the pipe is fragile on account of erosion this hit gets stronger. This hit makes a few quick waves and passes away quick, so it might cause various threats and harms in the pipelines. Generally, this bang hit within the pipeline projects has a crucial role and ignoring it leads to very large damages within the equipment.
Clogging of pipes and joints : Clogging happens when some sediment and objectives enter into the pipes and their components. This makes a condition in which the weak parts break.
Effect of temperature : At the point when the temperature is high, the obstruction of the pipes, especially the pipes with artificial material, for example, plastic, polyethylene segments, descends without question. When the depth is not suitable or the coverage is not enough, the low temperature causes freezing. This freezing makes some tension inside the pipes.
Poor quality connections and nonstandard plumbing : The loss of water is usually very much when unsuitable joints are used or incorrect piping is performed. Controlling these materials and performances can prevent loss of water, remarkably.
Leakages are inevitable part of the Water Distribution Network. Management of leakages plays a significant role in smooth functioning of the system.
Most of the leakage management related methods developed so far can be broadly classified as follows:
Leakage assessment methods which are focusing on quantifying the amount of water lost;
Leakage detection methods which are primarily concerned with the detection of leakage hotspots, and;
Leakage control models which are focused on the effective control of current and future leakage levels.
The loss of water is usually very much when unsuitable joints are used or incorrect piping is performed. Controlling these materials and performances can prevent loss of water, remarkably.
1. Leakage Assessment
The objective of leakage assessment (i.e. water audit) is to estimate the quantity of water lost in the system analyzed without worrying where the leaks are actually located. The assessment methods developed so far can be broadly classified into the following two main groups: (a) top-down leakage assessment methods and (b) bottom-up leakage assessment methods.
(a) Top Down Approach
The objective of top-down leakage assessment approaches is to estimate the leakage in a particular system by evaluating different components of the overall water balance, primarily the water consumed for different purposes. Despite the simplicity of a top-down type leak assessment, the leakage estimate obtained via this method is referred to as a crude estimate. Gathering such information helps to decide what the next step in leakage studies should be for a particular network but it does not help to bound potential leak areas, let alone locate leaks.
(b) Bottom-up Approach
Bottom-up type leakage assessment can be considered the second part of the audit process. This procedure is implemented when the company has confirmed the data used in the top-down portion. It includes every area of the company’s operation: billing records, distribution system, accounting principles etc. The audit’s main purpose is to find out the efficiency of the water distribution system and the measures needed to achieve these. Bottom-up audits require the most accurate and up-to-date data possible.
2. Leakage Detection Methods
Leakage assessment studies are carried out to quantify total losses including, real and apparent losses. This is followed by the development of leakage detection methods with the aim to detect and locate leaks. Detection methods are equipment or non-equipment based but it is common practice to use some leak detection method in conjunction with other methods.
(a) Leakage Awareness Methods
The term ‘leak awareness’ is used to explain the discovery of a leak in a particular area within the network. It does not give any information about its precise location. Usually a hydraulic model is needed for the leakage awareness test. Various hydraulic models have been proposed to detect leaks in water distribution systems. Those methods usually involve calibration/optimization techniques to analyze the different areas of the network.
(b) Leakage Localization methods
Leak localizing is an activity that identifies and proprieties the areas of leakage to make pinpointing of leaks easier. Some methods/techniques that belong to this group are: acoustic logging , step-testing , ground motion sensors and ground penetrating radars etc.
Leakage localization methods can be used on their own or before/following the application of some other method. For example, if a hydraulic model of the analyzed system is available then some numerical (i.e., inexpensive) leak detection method may be used before the leak localization method, to narrow the area searched for the leak. However, if the hydraulic model is not available (or not updated regularly) then a leak localization method could be used on its own.
(c) Leakage pinpointing methods
Leakage pinpointing methods include methodologies that are the most accurate in today's leak detection surveys. Three main groups described here are based on (a) leak noise correlators (b) gas injection and (c) pig-mounted acoustic sensing.
Leak pinpointing techniques are the most precise technologies currently available for leak detection. It should be remembered that such a precision comes with very high costs in terms of equipment owning or renting and man-hours needed for surveys to be carried out. Considering this and the length of time needed for implementation, it is recommended to use leak pinpointing techniques in conjunction with some leakage awareness or localisation method.
3. Leakage Control
Leakages in the water distribution systems not only wastes the precious resource but also impairs the service quality. Prompt awareness and effective control of leakage could enhance the supply security. Leakage control models can be generally classified into the following two main groups: (a) passive (reactive) leakage control and (b) active leakage control. A passive leakage control is a policy of responding only to leaks and bursts reported by the public (in some cases also by a company's own staff). Active leakage control concerns management policies and processes used to locate and repair unreported leaks from the water company supply system and customer supply pipes.
A scientific and rational leakage management strategy demands efficient, timely assessment and warning of leakages and Non Revenue Water (NRW) reduction. District Metered Areas (DMA) management, which is put forward by International Water Association (IWA) is as a tool for reducing the real losses. A district metered area (DMA) is defined as a discrete part of a water distribution network. It is usually created by closing boundary valves or by permanently disconnecting pipes to neighbouring areas. Water flowing in and out of the DMA is strictly controlled and metered in order to calculate the accurate water balance for each DMA. Based on the IWA water Balance, the NRW can be monitored to secure fast action and be the basis for planning the activities based on the highest return of investments in the future optimization of the water distribution network.
The key principle behind DMA management is the use of flow data to determine the level of leakage within a defined area of the water distribution network. This data allows the utility to react quickly to areas with high leakages and confirm and repair leaks instantaneously. The DMA will also make it possible to optimize water distribution in terms of energy consumption, pressure management and water quality issues. It was observed that a targeted leak detection program with active leakage monitoring of each DMA can in most places reduce the overall leakage in the distribution system by at least 40-50 %. However, how to build a DMA in practical terms and how to pinpoint the suspected leakage area precisely and quickly, are the common issues which every water utility is faced with.
Another important steps in leakage management is use of metering. Different types of water meters are installed by public water supply at the water source location as well as at the consumption points. In conjunction with volumetric pricing, metering can provide an incentive for water conservation. It helps to detect water leaks in the distribution network, thus providing a basis for reducing the amount of non-revenue water. There are several types of water meters in common use. The choice depends on the flow measurement method, the type of end-user, the required flow rates and accuracy requirements. Metering poses a financial burden not only during installation but also throughout the life cycle of meters.
Problems associated with metering arise particularly in the case of intermittent supply, which is common in many developing countries. Sudden changes in pressure can damage meters to the extent that many meters in cities in developing countries are not functional. Also, some types of meters become less accurate as they age and under-registering consumption leads to lower revenues if defective meters are not regularly replaced. Many types of meters also register air flows, which can lead to over-registration of consumption, especially in systems with intermittent supply, when water supply is re-established and the incoming water pushes air through the meters. Water meters do not distinguish between air and water both are counted as fluid. Use of smart meters can help to reduce the problem. Smart meters can be read remotely and more frequently, providing instant access to water consumption information for both customers and water utilities instead of getting the water bills monthly or bimonthly.
In addition to this some preventive measures can be planned so as to minimize / avoid the leakages such as
Replacement of aging water supply pipes: Around 90% of leakage cases are from water service pipes (water pipes to supply water to individual households connected to water distribution pipes). Lead water pipes, which tend to cause water leakage much more frequently compared with currently used polyethylene pipes, are given an intensive priority for replacement.
Upgrading and improving water distribution system: This focuses on reducing the amount of water leakage as well as improving water supply quality by such measures as reducing cases of rusty water and low water pressure. Especially, replacing all asbestos cement pipes, which cause many water leakage incident cases.
Water pressure control by the water distribution management system: The purposes of this system are: -Reduction of water leakage by reducing excess water pressure, Early detection of abnormalities of water distribution and execution of countermeasures at an early stage by remote-control operation, Implementation of impartial water supply unaffected by topographical elevation differences through water flow rate control among water treatment plants (transferring water supply amount each other).
The water distribution management system contributes to the effective use of water resources and efficient water transportation considerably. The loss of water is usually very much when unsuitable joints are used or incorrect piping is performed. Controlling these materials and performances can prevent loss of water, remarkably.
Conclusion: Water shortages associated with the increasing world population and global climate change are a matter of worldwide concern. In order not to waste limited available water resources, the implementation of water leakage prevention measures is an urgent issue. On the other hand, to implement water leakage prevention measures, considerable cost and time is required. In order to manage the problem of leakages , initially the factors causing leakages should be identified and subsequently the leakage assessment followed by detection and control strategies should be adopted.
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