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This publication is available at https://www.gov.uk/government/publications/water-and-sewerage-companies-in-england-environmental-performance-report-2025/thames-water-epa-data-report-2025
This report provides company specific data and information on the Environmental Performance Assessment (EPA) metrics. It contains current year and historic performance data (as published at the time, based on data provided in part by the water and sewerage companies). For further information on what each EPA metric and performance star ratings mean see our EPA metric guide.
In addition to the EPA metrics, this report contains a section on event duration monitoring (EDM) of storm overflows. For a comparison between water and sewerage companies and wider regulatory information see the environmental performance of the water and sewerage companies in 2025 report.
We set targets for each EPA metric. Water and sewerage company performance is then given a red, amber or green (RAG) status:
red – significantly below target
amber – below target
green – achieved target
We review and revise thresholds every 5 years.
1. EPA metric status and performance star rating
Main facts
For 2025:
red status for 4 metrics, amber status for 0 metric and green status for 2 metrics
1 of 4 water and sewerage companies (out of 9) rated as poor performing (1 star)
Annual performance star rating after assessment of Thames Water’s performance across all EPA metrics
Year
Overall EPA star rating (out of 4)
Star rating description
2011
3 stars
Above average company
2012
3 stars
Above average company
2013
2 stars
Below average company
2014
3 stars
Above average company
2015
3 stars
Above average company
2016
2 stars
Company requires improvement
2017
3 stars
Good company
2018
3 stars
Good company
2019
3 stars
Good company
2020
3 stars
Good company
2021
2 stars
Company requires improvement
2022
2 stars
Company requires improvement
2023
2 stars
Company requires improvement
2024
1 star
Poor performing company
2025
1 star
Poor performing company
Annual percentage of red, amber or green (RAG) status EPA metric results for Thames Water
Graph note: there were 6 EPA metrics in the years 2011 to 2015, 2018 to 2021, and 2025. There were 7 EPA metrics in the years 2016, 2017, 2022, 2023 and 2024.
Annual number of EPA metrics and their RAG status results for Thames Water
Year
Number of metrics in EPA
Number of red metrics
Number of amber metrics
Number of green metrics
2011
6
0
2
4
2012
6
0
4
2
2013
6
1
3
2
2014
6
0
4
2
2015
6
0
2
4
2016
7
1
4
2
2017
7
0
4
3
2018
6
0
3
3
2019
6
0
2
4
2020
6
0
4
2
2021
6
2
2
2
2022
7
2
2
3
2023
7
2
2
3
2024
7
3
2
2
2025
6
4
0
2
2. Total pollution incidents (sewerage) metric (category 1 to 3)
Main facts
For 2025:
35 sewerage pollution incidents per 10,000km of sewer – this is rated as red
379 actual incidents (needed 212 or fewer to be rated as green)
108,980km sewer length – from financial year ending 2018 (this baseline is used in the EPA)
performance was better than the sector (41) for sewerage pollution incidents per 10,000km of sewer
1 of 8 water and sewerage companies (out of 9) to be rated red
Annual number of pollution incidents (category 1 to 3) from Thames Water sewerage assets, with EPA status
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
green
amber
amber
amber
green
Incidents per 10,000km sewer
38
68
90
76
38
Actual incident numbers
258
468
612
517
263
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
amber
amber
amber
Incidents per 10,000km sewer
33
28
27
30
27
Actual incident numbers
357
303
297
325
292
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
amber
amber
amber
red
red
Incidents per 10,000km sewer
25
30
32
43
35
Actual incident numbers
271
331
350
470
379
Annual number of pollution incidents (category 1 to 3) from Thames Water sewerage assets, also showing EPA status and thresholds
Graph note: the EPA RAG status thresholds are set for normalised (per 10,000km sewer) numbers of sewerage incidents (see our EPA metric guide). We review and revise thresholds every 5 years. Equivalent thresholds for actual incident numbers are calculated using water and sewerage company sewer length data – these are shown in the graph background and the table below.
EPA thresholds for actual number of Thames Water sewerage incidents for the calendar years 2011 to 2025
Calendar year
Red status
Amber status
Green status
2011 to 2015
885 or above
346 to 884
345 or below
2016
542 or above
280 to 541
279 or below
2017 to 2020
543 or above
280 to 542
279 or below
2021
453 or above
257 to 452
256 or below
2022
431 or above
246 to 430
245 or below
2023
409 or above
235 to 408
234 or below
2024
398 or above
224 to 397
223 or below
2025
376 or above
213 to 375
212 or below
Number of pollution incidents (category 1 to 3) from Thames Water sewerage and water supply assets in 2025
Asset type
Number of pollution incidents (category 1 to 3)
Combined sewer overflow
1
Foul sewer
200
Other water industry premises
1
Pumping station
16
Rising main
18
Sewage treatment works
116
Storm tank
1
Surface water outfall
26
Water distribution system (water supply)
84
Water treatment works (water supply)
1
Note: water distribution system and water treatment works (both water supply assets) are not part of the EPA total pollution incidents (sewerage) metric.
Number of pollution incidents (total and breakdown of categories 1 to 3) from Thames Water sewerage and water supply assets in 2025
Asset type
Category 1 to 3
Category 1
Category 2
Category 3
Combined sewer overflow
1
0
0
1
Foul sewer
200
0
11
189
Other water industry premises
1
0
0
1
Pumping station
16
0
1
15
Rising main
18
0
1
17
Sewage treatment works
116
0
7
109
Storm tank
1
0
0
1
Surface water outfall
26
1
1
24
Water distribution system (water supply)
84
0
2
82
Water treatment works (water supply)
1
0
0
1
3. Serious pollution incidents (sewerage and water supply) metric (category 1 and 2)
Main facts
For 2025:
24 serious incidents – this is rated as red (needed 1 or fewer to be rated as green)
22 serious incidents from sewerage assets
2 serious incidents from water supply assets
1 of 7 water and sewerage companies (out of 9) to be rated red, no companies rated green
Annual number of serious pollution incidents (category 1 and 2) from Thames Water assets (sewerage and from 2021 including water supply), with EPA status
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
amber
amber
amber
amber
amber
Serious incidents per 10,000km sewer
2.9
2.2
3.2
2.3
1.8
Actual serious incident numbers – sewerage
20
15
22
16
12
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
amber
amber
amber
Serious incidents per 10,000km sewer
0.9
0.9
0.8
1.4
1.2
Actual serious incident numbers – sewerage
10
10
9
15
13
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
red
red
red
red
red
Serious incident numbers – all assets
12
17
14
33
24
Serious incident numbers – sewerage
12
17
13
33
22
Serious incident numbers – water supply
0
0
1
0
2
Annual number of serious pollution incidents (category 1 and 2) from Thames Water assets (sewerage and from 2021 including water supply), also showing EPA status and thresholds
Graph note: for 2011 to 2020 EPA RAG status thresholds were set for normalised (per 10,000km sewer) numbers of serious sewerage incidents (see our EPA metric guide). Equivalent thresholds for actual serious sewerage incident numbers were calculated using water and sewerage company sewer length data. We review and revise thresholds every 5 years. For 2021 to 2025 water and sewerage companies are in one of two groups with different thresholds set for actual serious sewerage and water supply incident numbers. The thresholds for actual serious incident numbers are shown in the graph background and the table below.
EPA thresholds for number of serious incidents from Thames Water assets (sewerage and from 2021 including water supply) for the calendar years 2011 to 2025
Calendar year
Red status
Amber status
Green status
2011 to 2015
27 or above
11 to 26
10 or below
2016 to 2020
16 or above
7 to 15
6 or below
2021 and 2022
6 or above
4 or 5
3 or below
2023 and 2024
5 or above
3 or 4
2 or below
2025
4 or above
2 or 3
1 or 0
Number of serious pollution incidents (category 1 and 2) from Thames Water sewerage and water supply assets in 2025
Asset type
Number of serious pollution incidents (category 1 and 2)
Combined sewer overflow
0
Foul sewer
11
Other water industry premises
0
Pumping station
1
Rising main
1
Sewage treatment works
7
Storm tank
0
Surface water outfall
2
Water distribution system (water supply)
2
Water treatment works (water supply)
0
4. Self-reporting of pollution incidents (sewerage and water supply) metric
Main facts
For 2025:
80% of all incidents self-reported, 98% from just pumping stations (PS) and sewage treatment works (STW) combined – this is rated as green
369 self-reported incidents, 95 incidents reported by others
performance was worse than the sector (87%) for self-reporting of all pollution incidents
performance was better than the sector (93%) for self-reporting of just PS and STW pollution incidents combined
1 of 8 water and sewerage companies (out of 9) to be rated green
Annual self-reporting of pollution incidents (category 1 to 3) from Thames Water sewerage and water supply assets, with EPA rating
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
amber
amber
amber
amber
amber
Percentage of incidents self-reported
46
50
58
53
61
Number of incidents self-reported
123
240
359
280
164
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
green
green
amber
Percentage of incidents self-reported
67
73
76
78
63
Number of incidents self-reported
244
235
254
290
209
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
red
amber
amber
amber
green
Percentage of incidents self-reported
65
74
76
75
80
Number of incidents self-reported
199
293
300
392
369
Percentage of PS and STW incidents self-reported
81
94
93
90
98
Number of PS and STW incidents self-reported
65
92
124
164
129
Annual self-reporting of pollution incidents (category 1 to 3) from Thames Water sewerage and water supply assets, also showing EPA status and thresholds
Graph note: the EPA RAG status thresholds (for all sewerage and water supply assets) are shown in the graph background and in the EPA metric guide. We review and revise thresholds every 5 years. From 2021 the additional number in brackets is the self-reporting percentage for just PS and STW incidents combined. To achieve green status self-reporting for all assets must be 80% or above and for just STW and PS combined must be 90% or above.
Self-reporting of pollution incidents (category 1 to 3) from Thames Water sewerage and water supply assets in 2025
Asset type
Number of pollution incidents self-reported (category 1 to 3)
Number of pollution incidents not self-reported (category 1 to 3)
Combined sewer overflow
1
0
Foul sewer
137
63
Other water industry premises
0
1
Pumping station
15
1
Rising main
17
1
Sewage treatment works
114
2
Storm tank
0
1
Surface water outfall
17
9
Water distribution system (water supply)
68
16
Water treatment works (water supply)
0
1
Self-reporting of serious pollution incidents (category 1 to 2) from Thames Water sewerage and water supply assets in 2025
Asset type
Number of serious pollution incidents self-reported (category 1 to 2)
Number of serious pollution incidents not self-reported (category 1 to 2)
Combined sewer overflow
0
0
Foul sewer
7
4
Other water industry premises
0
0
Pumping station
1
0
Rising main
1
0
Sewage treatment works
7
0
Storm tank
0
0
Surface water outfall
1
1
Water distribution system (water supply)
1
1
Water treatment works (water supply)
0
0
5. Discharge permit compliance (numeric) metric
Main facts
For 2025:
88.2% numeric discharge permit compliance – this is rated as red (needed 4 or fewer non-complaint treatment works to be rated as green)
34 permitted discharge outlets from water treatment works (WTW) – 97.1% compliance (1 non-compliant WTW)
performance worse than the sector (97.4%) for numeric discharge permit compliance
1 of 2 water and sewerage companies (out of 9) to be rated red
Annual discharge permit compliance (numeric) for Thames Water (STW and from 2016 includes WTW), with EPA status
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
green
green
red
amber
green
Percentage permit compliance
99.7
99.1
95.7
98.9
99.1
Number of permitted discharge outlets from STW
345
345
350
348
346
Number of non-compliant STW
1
3
15
4
3
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
green
green
green
green
Percentage permit compliance
97.9
99.5
99.0
99.7
99.7
Number of permitted discharge outlets from STW
349
348
349
349
349
Number of permitted discharge outlets from WTW
34
35
35
36
36
Number of non-compliant STW
6
2
4
1
1
Number of non-compliant WTW
2
0
0
0
0
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
green
green
green
amber
red
Percentage permit compliance
99.0
99.5
99.2
98.7
88.2
Number of permitted discharge outlets from STW
348
348
348
347
348
Number of permitted discharge outlets from WTW
36
36
36
35
34
Number of non-compliant STW
3
1
3
4
44
Percentage compliance STW
99.1
99.7
99.1
98.8
87.4
Number of non-compliant WTW
1
1
0
1
1
Percentage compliance WTW
97.2
97.2
100
97.1
97.1
Annual discharge permit compliance (numeric) for Thames Water (STW and from 2016 includes WTW), also showing EPA status and thresholds
Graph note: the EPA RAG status thresholds are shown in the graph background and in the EPA metric guide. We review and revise thresholds every 5 years.
6. Delivery of the Water Industry National Environment Programme (WINEP) metric
Main facts
For the financial year ending March 2026 (cumulative progress years 1 to 5 of the WINEP):
24.5% EPA schemes completed within planned deadlines – this is rated as red (needed 100% to be rated as green)
34 EPA schemes completed within planned deadlines
105 EPA schemes did not meet requirements within planned deadlines – 86 water quality, 11 water resources
performance was worse than the sector (80.2%)
1 of 4 water and sewerage companies (out of 9) to be rated red
264 non-EPA WINEP schemes completed out of 271 planned – 72.7% total WINEP delivery (EPA and non-EPA schemes)
Annual delivery of the WINEP (National Environment Programme up to the financial year ending 2020) by Thames Water, with EPA rating
Data for financial years ending 2012 to 2016
Financial year ending
2012
2013
2014
2015
2016
Asset Management Plan (AMP)
AMP5
AMP5
AMP5
AMP5
AMP6
EPA status
green
amber
green
green
green
Percentage of NEP complete to date (cumulative)
109
96.8
102
102
100
Cumulative number of schemes completed during AMP period
49
60
87
130
10
Data for financial years ending 2017 to 2021
Financial year ending
2017
2018
2019
2020
2021
Asset Management Plan (AMP)
AMP6
AMP6
AMP6
AMP6
AMP7
EPA status
green
green
green
green
amber
Percentage of NEP/WINEP complete to date (cumulative)
100
100
100
99.3
98.0
Cumulative number of schemes completed during AMP period
64
133
172
265
48
Data for financial years ending 2022 to 2026
Financial year ending
2022
2023
2024
2025
2026
Asset Management Plan (AMP)
AMP7
AMP7
AMP7
AMP7
AMP8
EPA status
amber
red
red
red
red
Percentage of WINEP complete within deadlines (to date)
99.5
95.2
93.4
75.2
24.5
Cumulative number of schemes completed during AMP period
191
236
269
367
34
Cumulative number of water quality schemes completed during AMP period
179
219
247
327
30
Cumulative number of water resources schemes completed during AMP period
5
5
10
27
4
Cumulative number of fisheries, biodiversity and geomorphology schemes completed during AMP period
7
12
12
13
0
Annual delivery of the WINEP (National Environment Programme up to the financial year ending 2020) by Thames Water, also showing EPA status and thresholds
Table and graph note: AMP5 schemes that were completed early before their planned year were included in the cumulative delivery percentage (in some cases resulting in percentages over 100%). AMP6 and AMP7 schemes that were completed early before their planned year are not included in the cumulative delivery percentage until their planned year (cannot report over 100%). The EPA RAG status thresholds are in the EPA metric guide. We review and revise thresholds every 5 years.
7. Sludge disposal and use metric
Main facts
For 2025:
100% satisfactory sludge disposal and use – this is rated as green
229,706t (tonnes dry solid) total volume dispatched
36,219ha (hectares) land used by them for spreading
82.76% of sludge dispatched was used by them in agriculture
1 of 8 water and sewerage companies (out of 9) to report 100% satisfactory sludge disposal and use – all water and sewerage companies rated green
Annual compliance with sludge disposal and use metric by Thames Water, with EPA ratings
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
green
green
green
green
green
Percentage of sludge compliant
100
100
100
100
100
Total volume of sludge dispatched (t thousands dry solid)
259.4
236.4
233.6
257.4
256.7
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
green
green
no data
no data
no data
Percentage of sludge compliant
100
100
no data
no data
no data
Total volume of sludge dispatched (t thousands dry solid)
260.0
230.9
222.4
203.1
211.0
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
no data
green
green
green
green
Percentage of sludge compliant
no data
100
100
100
100
Total volume of sludge dispatched (t thousands dry solid)
185.9
219.2
220.1
215.3
229.7
Table note: for the 2018 to 2021 calendar years, we suspended the metric from the EPA whilst we reviewed our regulatory regime for sludge. The EPA RAG status thresholds are in the EPA metric guide.
Annual summary of sewage sludge disposal and use (dry matter) by Thames Water
Year
Sewage sludge used by them in agriculture (t thousands)
Sewage sludge recovered by them non-agriculture (t thousands)
Sewage sludge disposed of by them or passed to other outlets (t thousands)
2021
184.5
1.4
0.0
2022
185.2
1.1
32.9
2023
178.2
4.4
37.5
2024
168.3
8.6
38.5
2025
190.1
2.9
36.7
8. Event Duration Monitoring (EDM) delivery
We have published the EDM storm overflow annual return dataset received from water and sewerage companies. This shows how often and how long the monitored storm overflows operated during 2025. The dataset also includes water and sewerage company reasons for performance issues with monitors and reasons for high spill counts.
Thames Water storm overflows
Year
2025
Total number of active storm overflows listed in the annual return
580
Total number of active storm overflows with EDM commissioned
580
Percentage of active storm overflows listed with EDM commissioned
100%
Total number of storm overflows with spill data
579
Percentage of storm overflows listed with spill data
99.8%
Average number of spills per storm overflow with spill data
15.9
Average duration (hours) per monitored spill event
11.7
Percentage storm overflows with ≥90% EDM operation during reporting period
