News
Leakage explained.
The ability to better manage water supplies is becoming increasingly important as demand for water continues to escalate. Even in the UK which enjoys a wetter climate than many global regions concerns about water availability, particularly in the light of the recent freak droughts have led to increased investment in the countries water production and distribution infrastructure.
Safeguarding against future water shortages is not just about producing enough water to meet demand, equally important is the need to control the amount of water that is lost in transit between the point of production and the end user.
Losses attributable to water leakage are a major concern in any water network, even a small leak could potentially result in the loss of thousands of litres of water if left undetected. Given that each litre of this wasted water has been treated and energy has been expended pumping it around the network, such losses also represent lost revenue for water operators. Furthermore the challenges presented by the Government’s Carbon Reduction Commitment (CRC) scheme means there is now even greater pressure on water operators to minimise energy wasted on treating and pumping additional water supplies to replace lost water. As such leakage us a pressing issue that needs to be carefully tackled and controlled in order to minimise its impact on the bottom line.
What is leakage? –Although it varies in magnitude from country to country leakage is common to every water network, the term is used to describe the water lost from pipes, joints and fittings and overflowing services reservoirs. As such it is one of the categories within the catch-all description of total water loss which itself describes the difference between the total amount of water going into a distribution network compared to the amount that is consumed and billed for.
During the 1990’s the UK’s National Leakage Initiative (NLI) developed two main approaches to identifying and quantifying leakage, the first known as the “water balance” accounts for every aspect of the water supplied to the network, as such it encompasses both sources of supply such as reservoirs and the mains distribution network. The second approach is the “burst and background estimates (BABE) approach, this method entails creating models than can be used to predict potential losses based on specific characteristics within a set leakage management policy.
Leakage generally falls into two categories – background leaks and bursts or breaks – Background leakage is the aggregation of losses from all the fittings on the network, such leaks are typically too small to detect individually. Burst leakage – this occurs from holes or fractures within the network that can be located using a range of specialist leak detection equipment. While major bursts and gushes on the surface may be reported to water companies by the public it is vital to keep on top of other less obvious leaks. While most visible leaks may be losing water at a high rate they are usually reported and rectified quickly, lesser leaks may not result in such spectacular losses per hour but they can run undetected for far longer and often lead to higher overall losses. Although the size of a hole may often be tiny, in some case no larger than a pin, the extent of water losses through leakage can be considerable particularly where they go undetected for long periods of time. It is these types of losses rather than the more easily identifiable large scale losses that pose the biggest problem for water operators.
At this point it is important to emphasise that leakage can never be eliminated, the sheer scale of water distribution networks and the inherent difficulties in accessing pipework coupled with other factors such as supply pressure, age of pipework and soil characteristics means zero leakage can never be achieved. This point is illustrated by the fact that the UK’s water distribution networks, even following considerable countrywide investment and modernisation to exhibit an average leakage figure of around 15 – 25% equating to some 3,600 mega litres of lost water per day. Rather than striving to achieve zero leakage, the main concern of water operators should be to manage leakage as closely as possible.
What causes leakage? –Despite a raft of recent replacement and renewal works using modern plastic piping much of the country’s water mains are still from iron or lead, with some dating back to the Victorian era. Coupled with the high numbers of joints, fittings, interconnections and relatively short pipe runs that characterise even the most modern water distribution networks, presenting multiple opportunities for leaks to occur. These factors together with higher supply pressures mean than some degree of leakage is inevitable, generally leaks can be attributed to four main causes, namely: –
1) Higher supply pressures – Supply pressures that exceed the original parameters of installed pipework (particularly older pipework) can cause pipes and / or joints to rupture or burst.
2) Corrosion –Rusting of pipes, fittings and joints steadily reduces their integrity, eventually resulting in failure. Causes of corrosion can arise from both within the pipe such as acidic waters from upland areas and outside of the pipe where the external pipe wall is attacked by elements in the soil. In both cases the resulting corrosion can weaken the pipe wall reducing its ability to withstand the supply pressure and leading to eventual failure.
3) Erosion – This problem often occurs where a leak has already formed, jets of water from the leak collect sand or stones from the installation environment which then hit the pipe, gradually weakening it and increasing the likelihood of a secondary leak.
4) Soil characteristics – Changes in the soil characteristics at the point of installation can have a material impact on the pipeline. Changes in temperature and moisture can cause the soil to expand and contract, potentially causing the pipeline to bend, movements in the soil can also cause movement of the pipeline and its associated fittings, increasing the risk of damage and failure.
Reducing the amount of water lost through leakage depends on both the distribution pressure and the amount of time taken to address a leak. Where losses stem from relatively small but steady leaks from a joint or fitting, such leaks can be especially hard to detect, particularly where the installation environment prevents water from rising to the surface. Controlling and minimising the consequences of a leak therefore requires close monitoring and detection of potential water leaks at the earliest possible stage.
Consequences of “lost water” – For every litre of water lost in a water network another litre of water has to be treated and pumped through the distribution network to compensate. With the UK consuming an estimated 9,000 mega litres of water per day the impact this can have on the cost of production and the available water supply quickly becomes evident. Just taking the energy costs by way of illustration, around 65% of Thames Waters yearly electricity consumption can be attributed to pumping water and sewerage across the Thames Region.
With water currently in plentiful supply in the UK the issue of water leakage is one which often tends to arouse public interest only when the supply become restricted, when water companies attempt to introduce higher water prices or water demand saving measures like compulsory metering. For water companies however the issue is an ongoing one, having an impact on key areas of their operations, including: –
Profitability –Water lost from pipelines means more water needs to be treated, pushing up costs, for example if leakage accounted for 50% of a water companies production then the cost of treatment including energy consumption in terms of pumping and electricity will have doubled. The increased need for water treatment may also mean that more water treatment plants are built than is necessary incurring excessive capital investment and reducing profitability.
Reduced customer satisfaction and impaired public image – In the UK access to a constant supply of treated water is regarded as an automatic right, failure to provide such access either because of failed water mains or a reduced water supply in times of drought can lead to reduced customer satisfaction and an increased interest in water leakage issues, these can often have a detrimental impact in a water companies public image.
Reduced resources – Detecting and repairing damage caused by water leakage can put a strain on resources, requiring water companies to prioritise which leaks most urgently need to be addressed. Limitations on the resources available to find and repair leaks can be particularly problematic where damage is being caused by small-scale leaks over long periods of time, as these leaks are difficult yo detect they can cause extensive damage before they are found, leading to the collapse of roads and / or footpaths.
Tackling leakage –The importance of the above factors puts the onus on water operators to employ a continuous leakage management strategy, such strategies can be passive where the amount of water in the network is ensured over time to determine overall levels of leakage, activewhere a strategy is employed to identify and tackle specific leakage points or a combination of the two. Which ever tactic is chosen the starting point for any leakage management programme is to ascertain the overall characteristics of the network, including factors such as age, installation and operating pressures.
A key weapon against leaks –District metering is a key weapon in the war against leaks, the concept of District Metered Area (DMAs) was first introduced to the UK at the start of the 1980s by the UK Water Authorities Association. A district is a defined area of the distribution system than can be isolated by boundary valves and for which the quantities of water entering and leaving can be metered. The subsequent analysis of flow and pressure, especially at night when a high proportion of users are inactive enables leakage specialists to calculate the level of leaks in the district. This can be used to determine not only whether work should be undertaken to reduce leakage, but also to compare levels of leakage in different districts and thereby target maintenance teams into those areas where they will have the greatest impact.
Even new distribution networks experience both types of leaks and the water industry in the UK must work with some of the oldest underground assets in the world, so it is completely unrealistic to expect to reduce total losses to zero in Britain’s mains network which runs to over 300,000km. However, the role of DMAs is to divide the network into manageable sections that make it easier to determine where bursts are and to repair them.
District metering is now part of an established active leak management programme among UK water companies, typical districts cover somewhere between 1,000 and 2,000 properties in urban areas, however coverage is by no means comprehensive, especially in more rural areas.
A developing role for DMAs –The role of the DMAs is changing as the leak management agenda progresses, initially DMAs are used as a tool to drive down leakage in networks that had received little or no previous leak detection work, apart from dealing with reported problems. At this stage their role is to highlight those areas where companies should be concentrating their efforts, helping to get the biggest benefit for a given maintenance budget. As work progresses and bursts are located and repairs DMAs make the resulting successes easier to measure, since any improvements should be more noticeable when viewed locally rather than by taking a snapshot of the distribution network as a whole. Eventually the repair work reaches the point where the DMAs are being used to look out for fresh leaks as they spring up.
In an ideal situation it should be possible to estimate the level of leakage using a “top down” water balance. This requires an assessment of total customer use which can then be subtracted from the total flow into the system the difference equates to the leakage. This approach is difficult to apply in most areas, largely because there are very few DMAs in which all the properties are metered, this makes it impossible for water companies to get a sufficiently accurate picture of consumption. The situation is changing slowly, especially in areas of particular water scarcity where compulsory metering is either being mooted such as Thames Water’s request for compulsory metering in all homes sold in Bromley and Croydon from 2010 or made mandatory by Government Legislation. Most water companies therefore favour the option of a “bottom up” approach which relies on metering the flows in and out of a district at night.
Using the data collected from night time flow measurements commonly known as night lines, enables water operators to accurately spot any unexpected continual increases in a DMA’s water consumption that might suggest a burst or an undetected leak. Best practice analysis of DMA flows requires the estimation of leakage when the flow is at its minimum, which is typically at night. Leakage teams close boundary valves around the DMA and take very accurate readings at around 3:00 or 4:00am which is generally the time when night flow is at its lowest. Customer demand is typically at a minimum at night and the percentage of the flow made up of leaks is therefore at it highest.
Low flows present a challenge – Under registration of flows is a significant challenge, many water companies are still relying on traditional mechanical DMA flow meters which cant cope with the low flows they need to measure at night, for example: –
Typical mixed commercial and domestic urban DMA will have two or three inward feeds and two or three pipes exiting the area, each feed line might expect typical flows of the order of 60m3 per hour in the daytime, the corresponding flow at night could drop as low as 2m3 per hour with low leakage. With a typical turn down ratio of only 40:1 mechanical meters sized to deal with the peak demands simply cannot provide the necessary accuracy. With the recent economic downturn this problem is exacerbated in areas where heavy industry has given way to commercial developments and housing. The overall level of consumption in such areas often falls to a fraction of the historical industrial demand, leaving mains pipes and flow meters hopelessly over-sized for the job, so-called “right sizing” programmes are an attempt by water companies to overcome this problem.
These are just some of the reasons why many water companies are upgrading their district meters to electromagnetic technology, Electromagnetic meters offer improved accuracy over a far superior range of flows. For example: – ABB AquaMaster meters offer +/-0.5% uncertainty and a dynamic turn-down range of 1000:1, in fact the results available today are such that these meters could even detect a toilet flushing.
Easy access –Installing and accessing DMA meters can be difficult, especially in busy urban areas where the ground is already crowded with an array of underground assets or where a pipeline runs under a major road. Conversely, meters in remote areas may be nowhere near a potential power supply. Thankfully, today’s battery technology means that meters such as the AquaMaster can be sited pretty much anywhere, without having to worry about the availability of power supplies or the need to frequent access. Accessing the data is the next challenge but the latest technology can help here too for example, ABBs AquaMaster Explorer transmitters have flow and pressure measurement capabilities, integral data loggers with possibilities of 1 minute logging and GSM text messaging so that leakage managers can collect all the flow and pressure data from the night lines from the comfort of the office.
Water companies face significant challenges in setting up and applying DLAs successfully, but there is now a growing body of experience in dealing with all issues. WRc is a great source of further information, it has carried out many meter technology comparison studies and developed a comprehensive set of Best Practice guides, these should be the first port of call for anyone involved in leakage management and meter replacement strategies.
ABB’s AquaMaster GSM flowmeter, the most technically advanced flowmeter in the world –With tens of thousands of units installed in the water industry, the AquaMaster flow meter has come a long way since the idea of applying electromagnetic technology to a market dominated by mechanical flow meters was first proposed within ABB. At that time in the late 1990’s water companies only used electromagnetic devices on large pipe diameter applications such as district mains and the idea of applying this approach to DMA leakage nd revenue applications was a new one. However ABB realised that a battery powered electromagnetic meter could exceed the current needs of the market for accuracy. With mechanical meters water companies were settling for an accuracy of +2%, but the metering experts at ABB knew that electromagnetic technology could beat this and save the water companies a lot of money in the process.
Even though there has not been any great demand from the water industry for better meters until that point confidential consultations with key customers convinced ABB that a new product could generate fresh demand from scratch. It is an easy case to make – improved accuracy will have a direct impact on water companies bottom lines. When compared with a conventional mechanical meter installation, a considerable amount of ancillary equipment including strainers, isolation valves and bypass is required in addition to the meter itself. The whole installation also has to be situated in a specially constructed chamber, taken together the requirement for the ancillary equipment and the chamber can add significantly to the cost of the installation.
In a typical AquaMaster installation on the other hand all that is required is the flow meter primary. A small chamber may also sometimes be required for the transmitter although it can also be located above ground in a pillar or kiosk housing. Consequently the cost of an AquaMaster installation can often be 60% less than a traditional mechanical meter installation. In addition to the lead-line in accuracy there are a number of other well known advantages to electromagnetic water metering when compared with mechanical devices. First, the fact that electromagnetic systems contain no moving parts eliminates the need for routine maintenance, this in turn means that the overall installation costs are lower and to this end the user does not need valves to isolate the meter during maintenance and replacement. The lack of moving parts also means that the electromagnetic flow readings will not deteriorate through wear, whereas a mechanical meters accuracy will deteriorate with age resulting in under reading, and with so many wearing parts a typical mechanical meter will have a useful life of just 5 years or possibly shorter if particulates are present in the water, while a correctly installed AquaMaster should offer fit and forget service for 10 years or more.
Enhanced revenue management –Consider a mechanical DN150 flow meter that is accurate to within +2%, this flow meter is installed in a line with an average flow rate of 10 litres per second which equates to an annual usage of 315,360m3. Assuming a cost just for water at £0.50 per m3 over the course of one year the potential inaccuracy of the meter could be losing the operator around £ 2,500 of revenue. If this meter is replaced with an ABB AquaMaster electromagnetic meter which has an accuracy of +0.5% then the meter could pay for itself within just 23 days and continue to save money in the future. Further savings and increased revenue come from the far wider flow turn down or operating range of an electromagnetic meter compared with a mechanical meter which gains additional revenue with night flows, where the flow rate normally drops and mechanical meters will stall and stop registering, this typically amounts to a similar sum, doubling the additional revenue to around £ 4,600 per annum.
The AQuaMaster was originally launched in London in 2001 in mains and battery powered versions, since that time the product has been regularly upgraded. Upgrades have included an improved safer battery avoiding Lithium and the recent addition of GSM/SMS technology, which enables users to remotely access up to date information from anywhere around the world. Using the same technology as a mobile telephone ABB AquaMaster flowmeters can now be contacted using a PC or laptop or through a mobile telephone via SMS messaging. Via a GSM link to their PC or laptop users can access the AquaMasters three integral data loggers, two of which collect data on flow and pressure, with the third providing daily flow totalisation. Data can be downloaded from the flow and pressure loggers based on both a 15 minute and a world leading high resolution one minute sample rate, to provide a range of information which can be used to pinpoint supply fluctuations and identify potential problems. Operators can also remotely reconfigure and maintain their AquaMaster units online, including adjusting the configuration, reading flow meter totals or performing diagnostic tests without the time and cost of dispatching an engineer or meter reader to carry out the work on site.
Using SMS text messaging operators can request updates on current flowmeter status simply by sending a text message to the AquaMasters telephone number. Via this medium operators can request and receive data on any of the meter parameters including flow rate, pressure, total water consumption, alarms and tariff totals.
Summary – As stressed at the start of this news item leakage in a water distribution network can never be completely eliminated, however experience has shown that combining an effective leakage management strategy with the latest technology can have a major positive impact on helping water operators to greatly reduce leakage in their networks.