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Our leakage performance

Our leakage performance

Update for July 2020

Round-the clock data from nearly 450,000 smart meters across London helped us find and repair a record number of leaks, hit our regulatory target and reduce overall leakage from our 20,000 mile network of pipes by 15 per cent last year.

Our final leakage reduction results for 2019/20 have now been audited and we’re pleased to confirm we were 11 million litres per day (Ml/d) under our annual target of 606 Ml/d.

Our hard work continues during the ongoing health pandemic, and we now have ambitious plans to continue modernising our network by ramping-up the use of advanced digital technology and smart data to achieve a further 20 per cent region-wide reduction in leakage by 2025, and 50 per cent by 2050.

Thames Water staff inspecting a smart meter outside

Steve Spencer, our operations director, explains: “We know reducing leakage and keeping the taps flowing are the most important things to our customers, and so these results are a huge step forward. Our smart upgrades combined with the dedication and commitment of our teams has delivered this boost in performance.

“Working with our customers, the data has given us a much greater understanding of what’s happening underground and saved millions of litres of water every day.

“We’re now determined to build on this momentum for another 20 per cent drop in leakage over the next five years, and then go further as part of ambitious long-term plans to replumb London and the Thames Valley. We know there’s no room for complacency as we face even tougher targets, and that’s why we’re investing in our people and the best technology to keep upgrading our network.”

Victoria Borwick, former Deputy Mayor of London and former MP, and independent monitor of Thames Water’s leakage reporting, adds: “Thames Water has increased its investment in tackling leakage by not only increasing the number of gangs working on the network, so that leaks can be repaired promptly to reduce wastage, but by also using sophisticated techniques, digital technology and smart meters to remotely measure the network more accurately.

“This increased focus on accurate data has increased ‘find and fix activity’ so that thousands of hidden leaks have been repaired, significantly reducing leakage.”

Smart water meters are being progressively installed across our region due to pressures on water resources from an increasing population and climate change. It’s the second biggest programme of its kind in the world, with the latest figures showing customers on a meter use up to 17% less water.

In 2019/20, meters helped detect 13,500 leaks on customer supply pipes and saved nearly 18 million litres every day, which is enough water to fill seven Olympic swimming pools. The meters provide 10 million readings every 24 hours and have so far been installed in 15 London boroughs, including Bexley, Camden, Hackney and Islington, with the remaining areas and Thames Valley due to be completed by 2025.

Find out more about metering at thameswater.co.uk/help/water-meters.

Thames Water’s action on leakage

We’re now building on our encouraging performance after receiving confirmation that we achieved our leakage reduction target for 2019/20. Despite the impact social distancing has had on our daily operations, our leakage level for the month of May was within 1Ml/d (0.2%) of our mid-range forecast and keeps us on track for our target this year. This is also six per cent lower than the same time a year ago, and part of a 37 per cent reduction in leakage between 2003/04 and 2019/20.

Read about our detailed May 2020 performance and see our 2019/20 monthly and annual average leakage levels at a glance.

Our ambitious plans centre around two key areas. First, innovation and improving the productivity of our leak repair work. Second, improving our data to help us work smarter.

Innovation and productivity

In 2019/20, we fixed almost 1,400 leaks every week on average. This figure has reduced to 978 in May 2020 due to the widespread impact of coronavirus, including restricted access to homes and social distancing guidance for the safety of our teams and customers.

Of the total number we fix, we know over a quarter of leaks are at our customers’ properties. While these are private leaks, outside of our vast network, we continue to work with our customers where possible to repair them – and in some cases we can do this free of charge.

As the majority of leaks we fix are hidden, our first challenge is finding them. To improve our efficiency and accuracy in doing this, we’re developing two digital data-driven tools. The first identifies our leakiest water supply zones and the second helps us locate the leaks in those zones more quickly. The tools automate the analysis of multiple dynamic data sources, using algorithms and models to support our leakage analysts and technicians. The output from these tools is a clear and simple visual display of leakage information, including an up-to-date map of our network, colour-coded to show the highest-risk pipes and pipe repair history.

To help make our repair processes even more efficient, we’ve brought in new ways of working and have created a data-driven performance management tool to help supervisors get the most from their repair teams. This involves a formal daily meeting structure between supervisors and scheduling teams, a standardised process and clarified responsibilities, as well as a bespoke ‘performance dashboard’ for supervisors that brings together key information about performance. Together with improvements to planning and scheduling of work, this enhanced performance management regime is expected to deliver a 12% efficiency improvement in ongoing leak repairs.

We’re also constantly looking for new technology and approaches to help us in our mission. For example, we’re doing this through:

  • Special in-pipe cameras to help locate difficult leaks.
  • ‘Fingerprinting’ our water zones to create a baseline and help us better understand where and why leakage occurs. Find out more in the innovation section of this month’s report.

Improving our data

To help us make good decisions on resources and leakage reduction initiatives, it’s important that we have the most accurate and up-to-date data possible. This is because our leakage figures are affected by more than just the water that leaks from our pipes.

A key part of updating our leakage data is refining the assumptions we make about water use by unmetered households, which is affected by factors such as population growth and housing developments. In the past we made these updates on an annual basis, but we’ve now changed the process to a six-monthly cycle and we’ll look to increase this frequency even further.

As part of this change, we’ve also taken a ‘big data’ approach to our analysis and have brought in new data to cross-reference against the information we already hold. This includes using the data from our smart meters to better understand the overall trends in our customers’ water use. We can then use that to inform our assumptions about water use by unmetered households. This is only possible because smart meters give us 24 readings every day, compared to the one or two readings per year we would have received for the same customers before their smart meters were installed.

Updating our data in this way is important as it will help us improve our leakage reduction capability and delivery. Having better data on where leakage is happening allows us to concentrate our detection and repair efforts on the parts of our network where we can reduce leakage the most.

Preliminary indications in September from this work suggested we had underestimated unmetered household demand, and therefore overstated our leakage figures as previously reported. The adjustment that was applied to our 2019/20 leakage figure as a result of this analysis, and following an in-depth review by external auditors, was larger than 20 Ml/d. Over the next few weeks we will be moving to a new leakage reporting methodology which will make leakage reporting more consistent across water companies. The move to the new reporting methodology means there will be some movement in our reported leakage level.

Therefore, rather than change our calculations for one report and for consistency of reporting with previous reports we have retained the smaller adjustment of 20 Ml/d this month. There is more detail about the leakage reporting changes later in this report.

In addition to the benefits noted above, we’re now using data from nearly 450,000 smart meters that are consistently providing us with better information about water use at all types of properties. For example, they highlight properties with a continuous flow of water, which is an indication of a possible leak. Using data in ways like this has helped to prevent 1 Ml/d of leakage since the start of April 2020.

We’ve also installed 27,000 acoustic loggers to date, which has helped us detect over 8 Ml/d of leakage since the start of April 2020.

Coronavirus impact on leakage performance

The ongoing coronavirus outbreak and resulting restrictions have had a significant impact on our leakage reduction activities and performance this month.

We’ve scaled down our efforts to find private leaks at our customers’ properties, primarily due to social distancing guidance. This work requires us to find out whether the leak is on the property’s internal or external pipework. To do this, often our engineers would need to access customers’ properties and come into direct contact with members of the household. Given the current government restrictions and the paramount importance of the health and safety of our customers and employees, we’ve suspended this activity – except in cases where it’s essential.

In addition, many of the repairs to our pipes are on public roads and pavements. Given the current restrictions and guidance, we have to take extra precautions when doing this work to protect both our key workers and members of the public, and this takes extra time.

Finally, due to the unprecedented nature and scale of the restrictions, we’ve seen a large reduction in water use over the night-time period that we use to calculate leakage. A large part of this reduction is caused by industries that have either suspended or scaled down their operations. To correct for this, we’ve adjusted our night usage estimates to improve the accuracy of our leakage level calculation. We continue to monitor this very carefully to ensure the night usage estimates are as accurate as possible. This is a complicated task given the ever-changing restrictions we all face. As a result, we have applied a careful but conservative approach to calculate our leakage position. Once we are fully able to assess the impact of the restrictions on demand we will have a more accurate view.

Due to the significant impact of the coronavirus restrictions and the effects they have had on our ability to deliver the levels of leakage activity in our original 2020-21 plan, we have formulated a new revised plan. This takes into account the impacts noted above, and has scaled down activity for the first quarter of this year – most notably it includes a lower number of repairs to private leaks at our customers’ properties.

Get involved

You too can play an important part in helping us achieve our targets.


We’d like your feedback on our leakage performance information. Please get in touch to share your feedback, or to discuss how we may be able to make this report more accessible for you.

We’ve also started a conversation thread on our community platform to create further opportunities for you to talk to us and to each other, and share ideas on reducing leakage. We’re keen to engage with you in a meaningful way and we intend to use your feedback to improve our understanding of how leakage affects you, so that we can adapt our services to better meet your needs.

Leakage reduction - at a glance

Monthly leakage 2020/21

ML/d Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
Monthly leakage level 583  578                    
Mid range monthly leakage 604 577 563 558 554 549 553 569 617 666 666 603
Variance -21  1                    

Year-to-date average leakage 2020/21

ML/d Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
YTD average leakage 583  581                    
Upper forecast YTD average leakage 604 591 581 576 571 568 566 566 572 581 589 590
Variance -20  -10                    


1. The figures in the above tables are operational leakage data and therefore based on information from Thames Water source systems at a point in time. This data may be subject to a data refresh on a monthly basis and for year-end reporting.

2. The actual leakage level figures reflect the provisional 40 Ml/d adjustment from April 2020 to date relating to underestimated unmetered household demand (referenced in this report).

3.The 2020-21 plan has been uplifted by 20 Ml/d to be consistent with the 20 Ml/d adjustment.

Conclusion of Ofwat investigation – June 2018

Ofwat investigated our leakage performance in 2017. In August 2018, we agreed a package of financial and non-financial commitments with Ofwat under Section 19 of the Water Industry Act 1991. We refer to these as our Section 19 Undertakings.

As part of our Section 19 Undertakings we agreed to pay £120 million back to our customers. This money comes solely from Thames Water’s shareholders and will be reflected in customer bills. In order to clarify and improve how we report leakage we appointed Victoria Borwick, former Deputy Mayor of London and former MP, as an independent monitor of our monthly leakage reporting. Victoria brings highly relevant experience of reporting and communicating complex matters to the public. We are working with Victoria to provide external and independent feedback and challenge to how we engage with and improve customer understanding of our leakage targets and performance against these.

Tonia Lewis continues to fulfil the role of Undertakings Compliance Officer. This role is responsible for ensuring overall compliance with the Undertakings and providing regular updates to our Board and Ofwat. We provided our fourth 6-monthly review of our compliance against our Undertakings to Ofwat on 30 April 2020.

Helpful links

Find out more

Please see the further sections below for some helpful background information on leakage, as well as more detail about our performance and our leakage reduction plan.

The information provided is, to the best of our knowledge, accurate, but may be subject to change from time to time. The information does not represent formal annual regulatory reporting.