Our leakage performance

What is leakage?

Leakage is the amount of water lost from pipes across the water network.


How do we measure leakage?

To get our leakage figure, we take meter readings for the total volume of water into an area and deduct an estimate of our customers’ night-time water usage. We use night-time figures as this has the least impact on the leakage calculation - 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.

Boy swimming in swimming pool with lane ropes

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 absolutely 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 amount of leaks we find and fix
  • Leakage reduction - the amount of water saved from leaks fixed and other leakage reduction activity


Our August 2018 results

Leakage level

The graph below shows the actual amount of water lost from our network in August compared with our plan. Due to things like weather, in some months we expect average daily leakage to be higher than in others, and we factor this in to our plans. Extremely cold or very hot weather can also increase leakage.

For August 2018, our average leakage level was 675 Ml/d, which is 43 Ml/d more than we’d planned. This is the equivalent of losing 17 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.

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. This makes it challenging to plan how many we should complete each month.

The pie chart shows the split of the different types of leaks that we fixed in August 2018. 43% were hidden and had to be detected by our teams. 30% were visible and were reported by the public. August saw more visible leaks than usual because of the increase in pumping and ground movements caused by the hot, dry weather. However, the increase was less than in July as weather moved closer to normal for the time of year. We prioritise fixing these visible leaks in response to customer expectations and because they are normally larger leaks than the hidden leaks we find. This reduces the impact of these leaks on availability of water which is especially important in periods of high demand. The remaining 27% 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 August 2018. We averaged 1,376 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 even further, 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.

Leakage reduction

The graph below shows the actual amount of water saved in August compared with our plan. This includes the hidden leaks and customer leaks we fix, and other leakage reduction activities such as replacing our larger worn out pipes. We saved 34 Ml/d of water in August, which was 3 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 just short of 26,000 loggers and are repairing the leaks located as a result of the alarms 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 plans every 3 months.

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. We have recently appointed a Compliance Monitoring Officer and an Independent Monitor to ensure we comply with the obligations arising from the Ofwat investigation.

Read more

Helpful links

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.