The inherent limitations of achieving the Economic Level of Leakage means that leakage can never be totally eradicated. But it can be controlled. This article explains how and why water companies need to do more to manage leakage.
Cutting leaks in a water stressed world
Water scarcity is one of the major challenges of our age. As the climate changes and many landscapes become hotter and dryer while others see more rainfall, the distribution and availability of usable water becomes ever more important.
The situation is not helped by a growing global population, set to reach 9.8 billion by 2050. With an increasingly urbanized population, getting potable water to these growing numbers of people, efficiently and sustainably, is a major challenge.
Fresh water use has risen rapidly over the last century, rising six-fold since 1900 to reach some four trillion cubic meters per year by the early 21st century and yet the amount of freshwater available has not changed. 
Many countries across the globe are experiencing water stress, which is calculated by the World Water Resources Institute as freshwater withdrawals as a share of internal (renewable) resources. For example, if withdrawals are less than 10 percent of resources, then a country has low water stress. This is the situation in the UK, which has a figure of 5.53 percent. Greater than 80 percent is extremely high stress and some African countries have figures in the hundreds or even thousands of percent. 
With water sources being increasingly overused, it’s vital to ensure that the water treated and distributed at so high a cost, is not wasted.
The challenge of leaks
Despite the relatively high rainfall in the UK, we have no cause for complacency about our use of water. Much of the water distributed to consumers, a staggering 3.2 million cubic metres of water a day, escapes through leaks.
And that is just one country. Across the globe, the picture is just as bad. It is estimated that around 126 billion cubic metres of water are lost through leaks every year, the equivalent of over 50,000 Olympic sized swimming pools. For water companies, this represents an annual revenue loss of $40 billion a year. Some 24 percent of countries have a non-revenue rate of greater 40 percent, revenue that could otherwise be used to fund investments in water infrastructure.
These enormous water losses have to be replaced, treated and pumped again to maintain supplies to customers. This in turn uses more energy and resources, cutting the sustainability of water operations.
In England and Wales, Ofwat defines leakage as treated water lost from the distribution system. This includes water lost from the utilities’ distribution networks and supply pipe losses from consumers’ own pipes.
The number, extent and duration of leaks, as well as the difficulty in detecting and correcting them, are affected by factors such as the operational strategy of the water utility, for example how it manages and controls pressures in the network. The length of mains pipes, their composition and age also have an effect, as does whether a particular area has predominantly more urban or rural customers.
Part of the challenge is that most pipework leaks remain hidden underground. Losses stemming from relatively small but steady leaks from a joint or fitting, can be especially hard to detect. This can pose particular difficulties where the pipe installation prevents water from rising to the surface. Because many of these leaks go unreported, many thousands of litres of water can be lost before the leak is fixed.
A big cause of these ‘background leaks’ is elevated supply pressures. While pressure is high, water is forced out into any existing leaks. New leaks can be generated at any points of strain such as joints in the pipework. The danger is exacerbated by older pipe work which may have suffered from corrosion and wear.
It has been calculated that reducing pressures can have a significant effect on leakage. A factor here is the Fixed and Variable Area Discharges (FAVAD) concept proposed in 1994. The velocity of flow of a leak varies with a Coefficient of Discharge (Cd) and the square root of pressure, but the area of some leakage paths may also vary with pressure. In fact, a 50 percent reduction in pressure gives a 65 percent reduction in leak flow rate.
Counting the cost
Ofwat requires water companies to fix leaks and requires them to be reduced by 16% over the next five years. It does not require that 100 percent of leaks be repaired, which would be an impossible demand due to the significant costs of fixing leaks compared to the costs of not fixing them. For water utilities, the cost of not fixing a leak includes environmental damage, as well as the cost of developing new water resources to compensate for the water lost through leaks.
This approach is called the sustainable economic level of leakage or SELL and ensures consumers get the best value for money. SELL takes account not only of the long-term costs and benefits to the utility, but also external social and environmental leakage costs. These include the traffic disruption that will occur during pipe repair work, the carbon footprints and the risk to consumer health from leaking pipes with inadequate pressure.
Leaks can lead to higher operating costs because of increased pumping and chemical consumption in the waterworks. Water that has leaked from a water pipe can also find its way into sewers at lower levels, both contributing to higher pumping costs and increasing the load on the sewage treatment plant.
Leakage management strategies
Utilities can take three general approaches to leakage management, classified as passive control, regular survey and leakage monitoring in zones or sectors.
Passive control is the least sophisticated strategy and in practice is a reaction to visible leaks reported by customers or spotted by the company’s staff. As such, it is a first step to leak improvements by making sure all the visible leaks are repaired. It is often used in areas with plentiful or low-cost water supplies, particularly where the importance of hidden, underground leakage is not so well appreciated.
The second strategy of regular surveys takes on board various inspection methods applied in a methodical manner throughout the supply areas. The strategy involves listening for leaks on pipework and fittings or taking readings of flow rates to identify high-volume night flows. Data from nighttime flow measurements enables water companies to accurately spot any unexpected continual increases in water consumption, which might suggest a burst or an undetected leak.
Leakage monitoring is a strategy of monitoring the flows into defined zones or districts to measure leakage and prioritize which leak detection activities to conduct and where they should be applied. This is the most cost-effective strategy for leakage management and is now the one most widely practiced.
This system of measuring zonal flows covers a number of levels. It begins with measurements at the production end of the distribution system and terminates at the consumer’s meter, giving an estimate of consumption.
A number of district meter areas (DMAs) of 500-3000 properties are set up. These have permanently closed boundary valves and the flow into them is monitored. Further down the hierarchy, small leak location areas within each DMA, of around 500-1000 connections, are monitored. Here, boundary valves remain open except during a leak location exercise. The lowest step in the chain is the reading of individual consumer meters, both domestic and commercial.
The International Water Association (IWA) offers advice on zones. It recommends identifying those zones that have a frequency and number of repairs on both mains and service connections. These are where the greatest reductions are likely to be achieved. It is important that mains repairs and service connections are analyzed separately.
Sniffing out the leaks
It’s clear that the water industry needs to improve leakage rates. In order to control flow rates and pressures and thus leaks, we need to know where they are. This is where metering comes in.
Using data from nighttime flow measurements enables water companies to accurately spot any unexpected continual increases in water consumption, which might suggest a burst or an undetected leak.
Traditional mechanical meters do not offer the accuracy needed and cannot cope with the low flows seen at night. By contrast, electromagnetic flowmeters offer improved accuracy over a far superior range of flows. In fact, modern meters could even detect a toilet flushing.
An example is ABB’s AquaMaster4. Its built-in Data Logger runs at high speed, giving the user total flexibility to download logged data frequently, every fifteen minutes if needed. The user can then investigate, in precise detail, flow and pressure activity during a period of interest, at even higher time resolution. Such high-resolution data aids step testing, leakage detection and water network analysis.
Measurement of flows was a major factor in the ability of Scottish Water to reduce its leakages, saving a staggering 1,000 pipe bursts in three years.
New thinking and technologies are shaking up how water companies find leaks. One such technique is acoustic loggers. Fitted at intervals of 200-400 metres on distribution mains they are located entirely below ground. Each unit incorporates a sensor block, which ‘listens’ to vibrations from the pipe, and the logger itself. Data is automatically sent to the control room from the logger and each unit is tagged with its GPS location, so the information it provides can appear on a map. Alarms from two loggers are a good indication that a leak exists somewhere in the few hundred meters between their locations.
Other techniques involve laser beams transmitted through fiber optics. Vibrations caused by water leaving the pipe alter the refection of the laser beam pulse, signaling a leak.
Utilities are also turning to space detection to combat leaks. A technique originally designed to detect water on other planets can capture detailed images covering 3,500 square km at once. The imagery is analysed to detect leaks and unusual amounts of water. Positions of incidents are sent to a team of technicians on the ground, for follow up investigations and repairs.
If we are going to meet the challenge of global water scarcity water companies need to do more to manage leakage. We as consumers must all do their part too and think use water more efficiently. Low flush toilets, water efficient washing machines and taking showers instead of baths can all help.
If we could cut personal consumption to just 100 litres a day and reduce leaks by 50 percent, we would have enough water for 20 million more people, without taking any more from the environment.
Being prepared to detect leaks in new ways with new techniques shows commitment to solving the problem of water stress and helps convince customers that they should also play their part in solving it.