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. We’ll miss our target again 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.


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 May 2018 results

Leakage level

The graph below shows the actual amount of water lost from our network in May compared with our plan. It’s higher than our annual figure for 2017/18 because leakage levels change throughout the year. In some months we expect average daily leakage to be higher or lower than in others. Extremely cold or very hot weather can also have an impact.

In May 2018, our leakage level was 680.5Ml/d, which is 14.1Ml/d more than we’d planned. This is the equivalent of losing more than 5 Olympic sized swimming pools of water more than we planned, each day.

Our average leakage since the start of April 2018 is 690Ml/d, 4.2Ml/d above our plan. This gap is as a result of the cold weather we experienced in March 2018. We are committed to doing all we can to address this shortfall in the coming months and get back on track.

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 May 2018. 48.2% were hidden and had to be detected by our teams, 25.5% were visible and were reported by the public, and the remaining 26.4% were customer leaks. We work with our customers to repair their leaks free of charge.

Total number of leaks fixed

The graph below shows we fixed a total of 6,703 leaks in May 2018, that’s around 216 per day and replaces April 2018 as our best monthly performance for fixing hidden, customer and visible leaks since March 2011. The impact of the cold weather in March meant we needed to increase our activity even further and although we achieved a lot, we were behind on the number of jobs we intended to do.

We achieved this because we recruited more people to fix leaks in 2017/18 and made improvements to our planning process.

Leakage reduction

The graph below shows the actual amount of water saved in May compared with our plan. This includes all the types of leaks we fix, and other leakage reduction activities such as replacing our larger worn out pipes. We saved 40.64 Ml/d of water in May, which was 7.91 Ml/d less than we had planned, this is mainly because the leaks we have found were smaller than our plan so did not provided sufficient savings.

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’re installing 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’ve installed 18,000 loggers so far, and we plan to have 26,000 installed by the end of August 2018.

  • 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 found more leaks in 2017/18 than the previous year.

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 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 on track against our original plan, we’re slightly behind our revised plan.

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

In June 2018 we accepted the initial findings of an Ofwat investigation into our leakage performance and 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.

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.