Our leakage performance

What is leakage?

Leakage is the amount of water lost from pipes across the water network. We supply almost one third of the water used by people and businesses, in the UK each day, to ten million customers, through over 32,000 km of water pipes.

How do we measure leakage?

To get our leakage figure, we take meter readings for the total volume of water we supply into an area and deduct an estimate of our customers’ night-time water usage. The difference between supply and night-time use is what we record as leakage; all water companies use this method. We also take water pressure into account, as this affects the amount of water lost through leaks.

We measure leakage in millions of litres per day (Ml/d). As an idea of scale, an Olympic-size swimming pool (50m x 25m x 2m) contains 2.5 million litres of water.

What’s our target and how are we doing?

We’ve set annual leakage targets up to 2020. Leakage levels change throughout the year, so these targets are for average daily leakage. Our actual levels can be compared with our targets in the table below.

  2015/16 2016/17 2017/18 2018/19 2019/20
Annual leakage target (Ml/d) 649 630 620 612 606
Actual annual leakage level (Ml/d) 642 677 TBC - -
  2015/16 2016/17 2017/18 2018/19 2019/20
Annual leakage target (Ml/d) 649 630 620 612 606
Actual annual leakage level (Ml/d) 642 677 695 - -

The table shows we beat our target in 2015/2016 but missed it in 2016/17 and in 2017/18.

We’re committed to reaching our 2019/20 leakage target of 606 Ml/d and have a plan in place to get us there. We have also committed to reducing leakage by 15% by the end of 2025 and by 50% in the longer term.


How do we measure monthly results?

Our monthly results are broken down into three areas:

  • Leakage level - the amount of water lost each day
  • Leaks fixed - the number of leaks we find and fix
  • Leakage reduction - the volumes of leaks found and fixed


Our September 2018 results

Leakage level

The graph below shows the actual amount of water lost from our network, in September, compared with our plan. In some months, we expect average daily leakage to be higher than in others because of the weather or when demand for water is high, and we factor this in to our plans. Cold or very hot weather can also increase leakage.

For September 2018, our average leakage level was 679 Ml/d, which is 53 Ml/d more than we’d planned. This is the equivalent of losing 21 Olympic sized swimming pools of water more than we planned, each day.

This gap is as a result of the cold weather we experienced, in March 2018, and the hot and dry weather we experienced over the summer. In broad terms, the cold weather had two effects – leakage rose, because more bursts occurred, and even though we fixed a lot of the extra leaks it meant we started the year with more leakage than we planned – so we have to work harder to catch up. The hot, dry weather also had two broad effects – first, higher demand for water meant we increased the amount of pumping needed to maintain storage levels in our reservoirs. This increases pressure in the pipes which in turn increases the amount of water lost from existing leaks and means new leaks happen. Second, the very dry ground shrinks around the pipes, which can cause them to move and lead to more bursts and underground leaks.

We are committed to doing all we can to address this shortfall and start 2019/20 with leakage at a level that means we can meet our 2019/20 annual leakage target. Following the cold weather, in March 2018, (also known as Freeze/Thaw) we have published a report on how we plan for, manage and respond to incidents.

Leaks fixed

We fix three different types of leaks:

Hidden leaks - these are below the surface and aren’t easy to find. We find them using data, technology, and people

Customer leaks - these are within the boundary of a customer’s property

Visible leaks - these are easy to see, for example on pavements or roads

Finding and fixing hidden leaks has the biggest impact on reducing leakage. When we find a hidden leak, we don’t always know how big it is until we’ve dug the hole and fixed it.

The pie chart shows the split of the different types of leaks that we fixed in September 2018. 46% were hidden and had to be detected by our teams. 29% were visible and were reported by the public. Although there has been a reduction in the level of pumping required to meet customer demand, leading to lower pressure in the network, we continued to see more visible leaks than usual in September. We prioritise fixing visible leaks in response to customer expectations. The remaining 25% were customer leaks; we work with our customers to repair their leaks free of charge.

Total number of leaks fixed

The graph below shows how many leaks we fixed in September 2018. We averaged 1,479 each week. The impact of the cold weather in March and hot, dry weather this summer has meant we’ve needed to increase our activity beyond our original planned level. We achieved this because we recruited more people in 2017/18 to fix leaks and have made improvements to our planning process.

Reducing leakage

The graph below shows the estimated volume from fixing leaks in September, compared with our plan. This includes visible leaks, the hidden leaks and the customer-side leaks we fix. We estimate that we stopped leaks equivalent to 33 Ml/d of water in September, which was 6 Ml/d more than we had originally planned. We have recruited additional resource and increased the amount of equipment used to detect hidden leaks (‘loggers’) deployed in order to outperform our planned levels of activity. Unfortunately, despite this, we have not yet saved as much as we need to return leakage to our original planned levels as the very cold, and then very hot and dry weather have had a significant impact.


Our leakage reduction plan

Finding more leaks to fix

Fixing leaks is the most important activity to reduce leakage. To fix more hidden leaks, we need to find them on the network. We’re increasing the number of leaks we find through:

  • Customer water meters - When we install a customer meter, we can immediately identify if there’s a leak. Our programme to install smart water meters is the second largest in the world and will help protect future water supplies.
  • Installing acoustic loggers - Acoustic loggers listen for the noise water makes as it leaks from pipes. They help us to improve leak detection and find harder-to-locate leaks. We have now installed approximately 26,000 loggers and are repairing the leaks located as a result of the information that the loggers are generating.
  • More leak detection technicians - We now have more leak detection technicians working for us than ever before. They use data to judge where leaks are occurring and tell repair teams where to dig. As a result, we have found significantly more leaks in 2018/19, to-date, than over the same period the previous year.
  • We’re also testing innovative solutions such as using thermal imaging cameras attached to drones, infrared cameras on an aeroplane and high resolution satellite images.

Leakage reduction activities

To help reach our target by 2019/20, we have additional leakage reduction activities taking place.

  • Pressure management - We manage the water pressure within parts of our network to reduce the likelihood of pipes bursting. This also reduces the amount of water lost through existing leaks.
  • Mains replacement - We have a long-term programme of replacing or repairing worn pipes, and we prioritise the ones which may cause disruption if they burst or leak.
  • Accounting for all water used - We're continually trying to improve our estimate of water used from our network. This activity focuses on stopping illegal use (for example unlicensed standpipes and illegal connections), replacing faulty customer meters, and ensuring all properties are registered on our billing system correctly.

Reviewing and refining our plans

To make sure that we’re on target to recover leakage and meet our target in 2019/20, we monitor our performance weekly and have a detailed review of our leakage reduction plan every month.

The cold weather in March 2018, meant that we started the 2018/19 reporting year with more holes in our pipes and therefore higher leakage than we’d planned. To help us recover from this, we’ve needed a revised plan to fix these holes, on top of what we already had in place. Whilst we’re ahead of our original plan, we’re slightly behind our revised plan. We are reviewing all options to improve our leakage performance.

The biggest risk to us meeting our target in 2019/20 is the weather. As well as the impact of cold or hot conditions on the network, snow and other bad weather also disrupts travel and access for repairs. Also, the largest amount of leakage comes from hidden leaks but extreme weather can lead to more visible leaks. These are important to fix quickly, but divert resources away from fixing hidden leaks.

More information on our leakage performance

Download the pdf below to learn more about our leakage performance

How can you help?

Conclusion of Ofwat investigation – June 2018

Ofwat has investigated our leakage performance. We agreed to pay £120 million back to our customers. This money will come solely from Thames’ shareholders and will be reflected in customer bills up to 2025. In order to clarify and improve how we report leakage we have 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 will work 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. 

As part of the Section 19 Undertaking we agreed with Ofwat in August 2018, we have appointed John Gilbert to fulfil the role of undertakings compliance officer. This role will be responsible for ensuring overall compliance with the undertaking and providing regular update to our Board and Ofwat.

Read more

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The information provided is, to the best of our knowledge, accurate, but may be subject to change from time to time. The information has not been the subject of any assurance exercise or audit process and does not represent formal regulatory reporting.

Feedback: We welcome your feedback on our leakage performance information. Get in touch with your feedback.