District metering – the front line in the fight against leaks

ABB’s UK Flow Manager Tony Hoyle discusses the developing role of district metering in leakage management.

Water scarcity is affecting people around the world as rain patterns alter in response to climate change. The UK has got off pretty lightly so far compared with some less fortunate regions but. some water companies have already been forced to take drastic measures. Thames Water, for instance, is to build a huge desalination plant to serve 900,000 people, while Folkstone and Dover issued compulsory metering notices in 2006 in an attempt to control demand.

Leakage management is one approach that no water company operating in Britain today can afford to ignore. Great progress has already been made. Water UK reports that overall the industry in England and Wales has cut leakage by over 30% since 1995. For example, Thames Water is spending £190 million on finding and fixing leaks this year alone.

A key weapon against leaks

District metering is a key weapon in the war against leaks. The concept of District Metered Areas (DMAs) was first introduced to the UK at the start of the 1980s by the then UK Water Authorities Association.

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. It is not uncommon even for new distribution networks to experience both types of leak. So it is completely unrealistic to expect to reduce total losses to zero in Britain’s mains network, which runs to over 300,000 km. 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. As work progresses and bursts are located and repaired, 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. The metering accuracy required increases with each successive stage of the leak management programme.

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. Customer demand is typically at a minimum at night and the percentage of the flow made up of leaks is therefore at its highest.

However, certain urban areas are seeing an increase in activity at night, with nightclubs, late-night takeaways and the shift to 24-hour licensing. All this can lead to increased ‘leakage’ reporting when, in fact, increased flow rates could be the result of genuine rises in consumption at night.

Long-term reliability and verification
As well as offering a lower accuracy than electromagnetic meters when new, mechanical meters also present an issue of long-term reliability, since mechanical wear causes a progressive deterioration in performance. A DMA-based leak reduction programme can only be successful if the data is reliable, so this is another strong driver for water companies to switch.

Of course, reputable instrumentation manufacturers put a great deal of effort into ensuring that meters of all types are accurate as they leave the factory. But meters must be peridocially verified or calibrated to maintain confidence in their accuracy in the longer term.

Water Industry Regulators like the Environment Agency recognised the benefits of verification tools several years ago for abstraction metering. It encouraged robust metering regimes and required regular checking and verification certificates.

New technology which extends the reach of verification tools to mains and battery-powered flow meters could allow water companies and OFWAT to implement periodic verification of strategic DMA meters. This would provide an extra level of confidence in DMA leakage data.

Whichever technology is being used, correct installation is vital. For example, meters need sufficient runs of straight pipework up and downstream to deliver accurate results.

Easy access

Water companies face significant challenges in setting up and applying DMAs successfully, but there is now a growing body of experience in dealing with all the 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.

For more information please email moreinstrumentation@gb.abb.com or call 0870 600 6122 ref. ‘District Metering’.

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