Southern Water storm overflows in 2025
What the official annual return shows for Southern Water’s storm overflows in England, compared with 2024 and with the other water companies.
Summary
The 2025 annual return lists 977 storm overflows run by Southern Water in England. 975 have a usable spill count. Together they recorded 15,554 spills and 114,868 hours of discharge. The median outlet recorded 7 spills and 17 hours.
For a fair comparison with 2024, we use only the 794 outlets with a count in both years and a monitor that worked at least 90% of each year. Their spills went from 27,326 to 14,244, a fall of 48%. 595 recorded fewer spills and 100 recorded more.
175 outlets (17.9%) recorded no spills in 2025. 45 (4.6%) recorded 60 or more.
Southern Water’s median of 7 spills per outlet is the 8th highest of the 10 companies in the return. The England median is 11.
115 outlets had a monitor that worked for less than 90% of the year. Counts from those outlets may be low.
- 977
- Outlets listed
- 15,554
- Spills in 2025
- 7
- Median per outlet
- 114,868
- Recorded hours
How many spills each outlet recorded
Outlets with a usable 2025 count, grouped by the number of spills. The longest bar is the largest group.
- 0
- 175 17.9%
- 1 to 9
- 363 37.2%
- 10 to 19
- 154 15.8%
- 20 to 39
- 158 16.2%
- 40 to 59
- 80 8.2%
- 60 or more
- 45 4.6%
Spills over time
The median outlet run by Southern Water recorded 7 spills in 2025, against 11 across England.
794 outlets have a comparable count for both 2024 and 2025, with the monitor working at least 90% of each year. 100 recorded more spills, 595 fewer and 99 the same. Together they went from 27,326 to 14,244 spills, a fall of 48%.
Largest rises from 2024 to 2025
- Forest Road Denmead No 1 CSO - 1009410 → 36
- Medina Road Cowes CEO - 10853713 → 48
- Albany Road East Cowes CEO - 1160718 → 40
| Year | Outlets with a count | Total spills | Median per outlet | England median |
|---|---|---|---|---|
| 2025 | 975 | 15,554 | 7 | 11 |
| 2024 | 971 | 29,355 | 14 | 19 |
| 2023 | 891 | 27,621 | 17 | 20 |
| 2022 | 875 | 15,564 | 10 | 13 |
| 2021 | 875 | 17,620 | 10 | 19 |
| 2020 | 43 | 989 | 13 | 18 |
Earlier returns list fewer of these outlets, so totals are not comparable between years. The median per outlet and the like-for-like change are fairer comparisons. Counts are events, not volume.
Largest falls from 2024 to 2025
Only outlets with a count in both years and at least 90% monitor operation in each. Counts depend on rainfall as well as on the sewer network, so a fall does not show on its own that an overflow improved.
- Singleton Relief CEO - 108335146 → 0
- Hawkhurst North SSO - 115719213 → 76
- Kings Somborne SSO - 115725252 → 125
- Sittingbourne SSO - 115437142 → 19
- Alfriston CEO - 108359156 → 34
- Lavant No.1 SSO - 115745287 → 166
- Tangmere SSO - 115777128 → 10
- West Wellow SSO - 115727216 → 101
- Buriton CEO - 116096116 → 4
- Overton SSO - 115916144 → 36
Most spills in 2025
- 1Lavant No.1 SSO - 115745166spills
River Lavant & GW via Wetland
- 2Lidsey SSO - 115776157spills
Lidsey Rife
- 3Ham Lane Lewes New SSO - 115974155spills
The Tidal River Ouse
- 4Kings Somborne SSO - 115725125spills
Tributary of the River Test
- 5Hammerwood Road Ashurst Wood SSO - 115955104spills
Shovelstrode Stream
- 6West Wellow SSO - 115727101spills
River Blackwater
- 7Bexhill & Hastings CSO - 11539899spills
English Channel
- 7Burwash Common SSO - 11573099spills
River Dudwell
- 9Sea Road Littlehampton CEO - 10936897spills
Controlled Sea
- 9South Harting SSO - 11583097spills
Unnamed Tributary of River Rother
Most hours in 2025
- 1Lavant No.1 SSO - 1157453,583hours
River Lavant & GW via Wetland
- 2Kings Somborne SSO - 1157252,801hours
Tributary of the River Test
- 3Ham Lane Lewes New SSO - 1159742,485hours
The Tidal River Ouse
- 4Lidsey SSO - 1157762,407hours
Lidsey Rife
- 5Hammerwood Road Ashurst Wood SSO - 1159552,283hours
Shovelstrode Stream
- 6South Harting SSO - 1158302,201hours
Unnamed Tributary of River Rother
- 7West Wellow SSO - 1157271,303hours
River Blackwater
- 8Burwash Common SSO - 1157301,302hours
River Dudwell
- 9Mannings Heath SSO - 1157391,252hours
River Arun
- 10Halland SSO - 1159321,208hours
Ridgewood Stream
Waterbodies with the most spills
Total 2025 spills from outlets the return links to each waterbody. A waterbody with more outlets will usually have a higher total.
| Waterbody | Outlets | Spills | Spills per outlet |
|---|---|---|---|
| Solent | 43 | 880 | 20.5 |
| Medway | 86 | 707 | 8.2 |
| Sussex | 25 | 425 | 17 |
| Southampton Water | 39 | 368 | 9.4 |
| Medina | 9 | 319 | 35.4 |
| Lower Rother from Robertsbridge to Iden | 12 | 307 | 25.6 |
| Western Rother | 8 | 297 | 37.1 |
| Portsmouth Harbour | 36 | 262 | 7.3 |
| Rother | 10 | 248 | 24.8 |
| Lidsey Rife | 2 | 228 | 114 |
How to read this report
- A spill is a counted event under the 12/24-hour method. It is not a volume, and it does not measure harm or water quality.
- Missing counts are left out, not treated as zero. Low monitor operation can make a count too low.
- Rankings compare counts only. They do not show whether an overflow broke its permit or the law.
- Earlier years list fewer outlets, so compare medians or like-for-like groups, not totals.
Data: Environment Agency event duration monitoring annual returns, Open Government Licence v3.0. How spills are counted · How the data works · Sources