Data annex: water and sewerage companies in England serious pollution incidents (category 1 and 2) for 2016 to 2024
Published 18 July 2025
Applies to England
© Crown copyright 2025
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This data annex supports the water and sewerage companies pollution incident report for 2016 to 2024. It presents charts and tables with company specific data and trends for the annual number of serious pollution incidents (category 1 and 2).
1. Anglian Water
Anglian Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Anglian Water annual data – this identifies the years 2017, 2019 and 2021 to be significantly higher than the average for the data period 2016 to 2024.
Anglian Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 11 | - |
| 2017 | 19 | 13.3 |
| 2018 | 10 | 14.3 |
| 2019 | 14 | 11.7 |
| 2020 | 11 | 13.0 |
| 2021 | 14 | 12.0 |
| 2022 | 11 | 12.0 |
| 2023 | 11 | 9.7 |
| 2024 | 7 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
2. Northumbrian Water
Northumbrian Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Northumbrian Water annual data – this identifies the year 2016 to be significantly higher than the average for the data period 2016 to 2024.
Northumbrian Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 9 | - |
| 2017 | 3 | 4.7 |
| 2018 | 2 | 2.7 |
| 2019 | 3 | 3.0 |
| 2020 | 4 | 2.7 |
| 2021 | 1 | 1.7 |
| 2022 | 0 | 0.3 |
| 2023 | 0 | 0.0 |
| 2024 | 0 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
3. Severn Trent Water
Severn Trent Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Severn Trent Water annual data – this identifies the years 2016, 2018, 2019 and 2021 to be significantly higher than the average for the data period 2016 to 2024.
Severn Trent Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 7 | - |
| 2017 | 2 | 5.3 |
| 2018 | 7 | 4.3 |
| 2019 | 4 | 4.3 |
| 2020 | 2 | 3.3 |
| 2021 | 4 | 2.3 |
| 2022 | 1 | 1.7 |
| 2023 | 0 | 0.7 |
| 2024 | 1 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
4. Southern Water
Southern Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Southern Water annual data – this identifies the years 2021, 2023 and 2024 to be significantly higher than the average for the data period 2016 to 2024.
Southern Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 3 | - |
| 2017 | 4 | 4.7 |
| 2018 | 7 | 6.0 |
| 2019 | 7 | 6.0 |
| 2020 | 4 | 7.7 |
| 2021 | 12 | 7.0 |
| 2022 | 5 | 10.0 |
| 2023 | 13 | 11.0 |
| 2024 | 15 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
5. South West Water
South West Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to South West Water annual data – this identifies the year 2021 to be significantly higher than the average for the data period 2016 to 2024.
South West Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 4 | - |
| 2017 | 3 | 3.0 |
| 2018 | 2 | 2.0 |
| 2019 | 1 | 2.0 |
| 2020 | 3 | 4.0 |
| 2021 | 8 | 4.3 |
| 2022 | 2 | 4.0 |
| 2023 | 2 | 2.7 |
| 2024 | 4 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
6. Thames Water
Thames Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Thames Water annual data – this identifies the year 2024 to be significantly higher than the average for the data period 2016 to 2024.
Thames Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 10 | - |
| 2017 | 10 | 9.7 |
| 2018 | 9 | 11.3 |
| 2019 | 15 | 12.3 |
| 2020 | 13 | 13.3 |
| 2021 | 12 | 14.0 |
| 2022 | 17 | 14.3 |
| 2023 | 14 | 21.3 |
| 2024 | 33 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
7. United Utilities
United Utilities number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to United Utilities annual data – this identifies the years 2016, 2017 and 2024 to be significantly higher than the average for the data period 2016 to 2024.
United Utilities number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 4 | - |
| 2017 | 2 | 2.3 |
| 2018 | 1 | 1.0 |
| 2019 | 0 | 0.3 |
| 2020 | 0 | 0.3 |
| 2021 | 1 | 0.3 |
| 2022 | 0 | 0.7 |
| 2023 | 1 | 1.0 |
| 2024 | 2 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
8. Wessex Water
Wessex Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Wessex Water annual data – this identifies the years 2017, 2018, 2020, 2021, and 2022 to be significantly higher than the average for the data period 2016 to 2024.
Wessex Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 2 | - |
| 2017 | 3 | 3.0 |
| 2018 | 4 | 2.7 |
| 2019 | 1 | 3.0 |
| 2020 | 4 | 3.3 |
| 2021 | 5 | 4.7 |
| 2022 | 5 | 3.7 |
| 2023 | 1 | 2.0 |
| 2024 | 0 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.
9. Yorkshire Water
Yorkshire Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and trend 2016 to 2024
Chart note: a statistical assessment (using the Pearson correlation coefficient) has been applied to Yorkshire Water annual data – this identifies the years 2018 and 2024 to be significantly higher than the average for the data period 2016 to 2024.
Yorkshire Water number of serious pollution incidents (category 1 and 2) from sewerage and water supply assets, and 3 year moving average 2016 to 2024
| Year | Number of serious pollution incidents (category 1 and 2) |
3 year moving average |
|---|---|---|
| 2016 | 7 | - |
| 2017 | 6 | 9.0 |
| 2018 | 14 | 9.0 |
| 2019 | 7 | 8.0 |
| 2020 | 3 | 5.0 |
| 2021 | 5 | 3.7 |
| 2022 | 3 | 4.3 |
| 2023 | 5 | 7.0 |
| 2024 | 13 | - |
Table note: 3 year moving averages are presented for the middle year of each 3 years. The years 2016 and 2024 are included in calculations but do not have averages presented in the table as they are not middle years.