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 gives the most accurate leakage calculation – if we used day-time use, there would be much more variability in how much water is used, which would mask how much water had leaked. 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 2015/16 but missed it in 2016/17 and 2017/18. We’ll miss our target again in 2018/19.

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 June 2018 results

Leakage level

The graph below shows the actual amount of water lost from our network in June 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 June 2018, our leakage level was 686 Ml/d, which is 39.6 Ml/d more than we’d planned. This is the equivalent of losing more than 16 Olympic sized swimming pools of water more than we planned, each day.

Our average leakage since the start of April 2018 is 690 Ml/d, 20.8 Ml/d above our plan. This gap is as a result of the cold weather we experienced in March 2018 and the ongoing hot weather. We are striving to do 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 different types of leaks that we fixed in June 2018. 48.0% were hidden and had to be detected by our expert teams, 26.8% were visible and were reported by the public, and the remaining 25.3% were leaks on our customers’ pipes. We repair leaks in customer properties free of charge.

Total number of leaks fixed

The graph below shows we fixed a total of 5,562 leaks in June 2018, that’s around 185 per day. The impact of the cold weather in March and the hot weather in May and June meant we needed to increase our activity beyond our original planned level.

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 June compared with our plan. This includes all the types of leaks we fix, and other leakage reduction activities such as replacing our worn out pipes. We saved 35.09 Ml/d of water in June, which was 5.55 Ml/d more than we had originally planned. Unfortunately we’ve not saved as much as we’d have liked, so we are increasing our activity further.

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 doing all we can 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, in addition to what we already had in place.

The impact of the hot, dry weather we are currently experiencing has resulted in a further increase in reported leakage for June. Higher demand and subsequent higher pressures in our network to maintain supplies to customers, results more burst pipes and higher leakage. Customers use more water at night when the weather is hot, which is when we traditionally measure leakage. We are reviewing our night-time usage data to ensure our leakage is reported as accurately as possible. We also predict that the very dry ground will start to cause pipes to move and more bursts and underground leaks to occur.

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.