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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/southern-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 metrics 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 Southern Water’s performance across all EPA metrics
Year
Overall EPA star rating (out of 4)
Star rating description
2011
2 stars
Below average company
2012
2 stars
Below average company
2013
1 star
Poor performing company
2014
2 stars
Below average company
2015
3 stars
Above average company
2016
3 stars
Good company
2017
3 stars
Good company
2018
2 stars
Company requires improvement
2019
1 star
Poor performing company
2020
2 stars
Company requires improvement
2021
1 star
Poor performing company
2022
2 stars
Company requires improvement
2023
2 stars
Company requires improvement
2024
2 stars
Company requires improvement
2025
1 star
Poor performing company
Annual percentage of red, amber or green (RAG) status EPA metric results for Southern 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 Southern Water
Year
Number of metrics in EPA
Number of red metrics
Number of amber metrics
Number of green metrics
2011
6
2
1
3
2012
6
2
1
3
2013
6
3
0
3
2014
6
2
0
4
2015
6
0
3
3
2016
7
0
4
3
2017
7
0
4
3
2018
6
2
1
3
2019
6
3
1
2
2020
6
2
2
2
2021
6
4
1
1
2022
7
2
1
4
2023
7
2
1
4
2024
7
2
3
2
2025
6
4
0
2
2. Total pollution incidents (sewerage) metric (category 1 to 3)
Main facts
For 2025:
64 sewerage pollution incidents per 10,000km of sewer – this is rated as red
253 actual incidents (needed 77 or fewer to be rated as green)
39,729km sewer length – from financial year ending 2018 (this baseline is used in the EPA)
performance was worse 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 Southern Water sewerage assets, with EPA status
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
red
red
red
red
amber
Incidents per 10,000km sewer
221
189
148
135
75
Actual incident numbers
479
409
320
292
163
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
amber
red
red
Incidents per 10,000km sewer
35
31
39
110
102
Actual incident numbers
138
123
151
430
400
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
red
red
red
red
red
Incidents per 10,000km sewer
94
90
59
68
64
Actual incident numbers
372
359
234
269
253
Annual number of pollution incidents (category 1 to 3) from Southern 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 company sewer length data – these are shown in the graph background and the table below.
Graph and table note: the actual number of total pollution incidents for 2022 is different to the score published in our reports between 2022 and 2024. This is a result of subsequent audits and checking.
EPA thresholds for actual number of Southern Water sewerage incidents for the calendar years 2011 to 2025
Calendar year
Red status
Amber status
Green status
2011 to 2015
281 or above
110 to 280
109 or below
2016
197 or above
101 to 196
100 or below
2017 to 2020
194 or above
100 to 193
99 or below
2021
165 or above
94 to 164
93 or below
2022
157 or above
90 to 156
89 or below
2023
149 or above
86 to 148
85 or below
2024
146 or above
82 to 145
81 or below
2025
138 or above
78 to 137
77 or below
Number of pollution incidents (category 1 to 3) from Southern Water sewerage and water supply assets in 2025
Asset type
Number of pollution incidents
(category 1 to 3)
Combined sewer overflow
6
Foul sewer
75
Other water industry premises
0
Pumping station
70
Rising main
29
Sewage treatment works
69
Storm tank
0
Surface water outfall
4
Water distribution system (water supply)
47
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 Southern Water sewerage and water supply assets in 2025
Asset type
Category 1 to 3
Category 1
Category 2
Category 3
Combined sewer overflow
6
0
0
6
Foul sewer
75
0
2
73
Other water industry premises
0
0
0
0
Pumping station
70
0
1
69
Rising main
29
1
7
21
Sewage treatment works
69
0
1
68
Storm tank
0
0
0
0
Surface water outfall
4
0
0
4
Water distribution system (water supply)
47
0
0
47
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:
12 serious incidents – this is rated as red (needed 0 to be rated as green)
12 serious incidents from sewerage assets
0 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 Southern Water assets (sewerage and from 2021 including water supply), with EPA status
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
red
red
red
red
amber
Serious incidents per 10,000km sewer
9.7
4.6
4.2
5.5
3.2
Actual serious incident numbers – sewerage
21
10
9
12
7
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
red
red
amber
Serious incidents per 10,000km sewer
0.8
1
1.8
1.8
1.0
Actual serious incident numbers – sewerage
3
4
7
7
4
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
red
red
red
red
red
Serious incident numbers – all assets
12
6
13
15
12
Serious incident numbers – sewerage
12
6
13
15
12
Serious incident numbers – water supply
0
0
0
0
0
Annual number of serious pollution incidents (category 1 and 2) from Southern 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.
Graph and table note: the number of serious pollution incidents for 2022 is different to the score published in our reports between 2022 and 2024. This is a result of subsequent audits and checking.
EPA thresholds for number of serious incidents from Southern 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
9 or above
4 to 8
3 or below
2016 to 2020
6 or above
3 to 5
2 or below
2021 and 2022
4 or above
2 or 3
1 or 0
2023 and 2024
3 or above
2
1 or 0
2025
2 or above
1
0
Number of serious pollution incidents (category 1 and 2) from Southern 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
2
Other water industry premises
0
Pumping station
1
Rising main
8
Sewage treatment works
1
Storm tank
0
Surface water outfall
0
Water distribution system (water supply)
0
Water treatment works (water supply)
0
4. Self-reporting of pollution incidents (sewerage and water supply) metric
Main facts
For 2025:
84% of all incidents self-reported, 90% from just pumping stations (PS) and sewage treatment works (STW) combined – this is rated as green
254 self-reported incidents, 47 incidents reported by others
performance was worse than the sector (87%) for self-reporting of all pollution incidents
performance was worse 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 Southern Water sewerage and water supply assets, with EPA rating
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
green
green
green
green
amber
Percentage of incidents self-reported
84
86
77
69
59
Number of incidents self-reported
405
356
248
203
99
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
green
green
green
Percentage of incidents self-reported
71
70
83
87
88
Number of incidents self-reported
103
94
156
400
360
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
green
green
amber
amber
green
Percentage of incidents self-reported
90
90
69
82
84
Number of incidents self-reported
353
352
174
271
254
Percentage of PS and STW incidents self-reported
96
95
80
86
90
Number of PS and STW incidents self-reported
259
213
81
122
125
Annual self-reporting of pollution incidents (category 1 to 3) from Southern 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 Southern 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
4
2
Foul sewer
55
20
Other water industry premises
0
0
Pumping station
63
7
Rising main
23
6
Sewage treatment works
62
7
Storm tank
0
0
Surface water outfall
0
4
Water distribution system (water supply)
46
1
Water treatment works (water supply)
1
0
Self-reporting of serious pollution incidents (category 1 to 2) from Southern 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
1
1
Other water industry premises
0
0
Pumping station
1
0
Rising main
5
3
Sewage treatment works
0
1
Storm tank
0
0
Surface water outfall
0
0
Water distribution system (water supply)
0
0
Water treatment works (water supply)
0
0
5. Discharge permit compliance (numeric) metric
Main facts
For 2025:
96.7% numeric discharge permit compliance – this is rated as red (needed 3 or fewer non-complaint treatment works to be rated as green)
24 permitted discharge outlets from water treatment works (WTW) – 100% compliance (0 non-compliant WTW)
performance was 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 Southern Water (STW and from 2016 includes WTW), with EPA status
2011 to 2015 data
Year
2011
2012
2013
2014
2015
EPA status
red
amber
red
green
green
Percentage permit compliance
96.0
96.8
96.0
99.0
99.3
Number of permitted discharge outlets from STW
277
277
298
295
291
Number of non-compliant STW
11
9
12
3
2
2016 to 2020 data
Year
2016
2017
2018
2019
2020
EPA status
amber
amber
green
amber
amber
Percentage permit compliance
98.7
98.2
99.1
98.8
97.1
Number of permitted discharge outlets from STW
293
309
313
316
315
Number of permitted discharge outlets from WTW
11
19
20
20
25
Number of non-compliant STW
2
5
1
2
10
Number of non-compliant WTW
2
1
2
2
0
2021 to 2025 data
Year
2021
2022
2023
2024
2025
EPA status
red
amber
green
amber
red
Percentage permit compliance
97.9
98.2
99.4
98.2
96.7
Number of permitted discharge outlets from STW
315
313
312
315
310
Number of permitted discharge outlets from WTW
25
24
24
24
24
Number of non-compliant STW
6
6
2
5
11
Percentage compliance STW
98.1
98.1
99.4
98.4
96.5
Number of non-compliant WTW
1
0
0
1
0
Percentage compliance WTW
96.0
100
100
95.8
100
Annual discharge permit compliance (numeric) for Southern 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):
50.0% EPA schemes completed within planned deadlines – this is rated as red (needed 100% to be rated as green)
10 EPA schemes completed within planned deadlines
10 EPA schemes did not meet requirements within planned deadlines – 9 water quality, 1 FBG
performance was worse than the sector (80.2%)
1 of 4 water and sewerage companies (out of 9) to be rated red
17 non-EPA WINEP schemes completed out of 17 planned – 73.0% total WINEP delivery (EPA and non-EPA schemes)
Annual delivery of the WINEP (National Environment Programme up to the financial year ending 2020) by Southern 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
green
green
green
green
Percentage of NEP complete to date (cumulative)
124
109
100
100
100
Cumulative number of schemes completed during AMP period
124
190
200
267
2
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
red
red
Percentage of NEP/WINEP complete to date (cumulative)
100
100
100
90.0
87.2
Cumulative number of schemes completed during AMP period
80
113
137
207
34
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
green
green
amber
red
Percentage of WINEP to date complete within deadlines (to date)
98.4
100
100
98.5
50.0
Cumulative number of schemes completed during AMP period
127
255
258
574
10
Cumulative number of water quality schemes completed during AMP period
106
225
227
512
10
Cumulative number of water resources schemes completed during AMP period
3
4
5
30
0
Cumulative number of fisheries, biodiversity and geomorphology schemes completed during AMP period
18
26
26
32
0
Annual delivery of the WINEP (National Environment Programme up to the financial year ending 2020) by Southern 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
66,516t (tonnes dry solid) total volume dispatched
14,844ha (hectares) land used by them for spreading
100% 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 Southern 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)
101.4
59.5
64.0
61.0
50.9
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)
60.4
53.2
53.8
50.7
58.1
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
99.28
99.59
100
Total volume of sludge dispatched (t thousands dry solid)
59.0
60.0
59.2
58.6
66.5
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 Southern 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
59.0
0.0
0.0
2022
60.0
0.0
0.0
2023
59.2
0.0
0.0
2024
58.6
0.0
0.0
2025
66.5
0.0
0.0
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.
Southern Water storm overflows
Year
2025
Total number of active storm overflows listed in the annual return
977
Total number of active storm overflows with EDM commissioned
977
Percentage of active storm overflows listed with EDM commissioned
100%
Total number of storm overflows with spill data
975
Percentage of storm overflows listed with spill data
99.8%
Average number of spills per storm overflow with spill data
16.0
Average duration (hours) per monitored spill event
7.4
Percentage storm overflows with ≥90% EDM operation during reporting period
