United Utilities storm overflows in 2025

What the official annual return shows for United Utilities’s storm overflows in England, compared with 2024 and with the other water companies.

Map of every United Utilities outlet England 2025 report

Summary

The 2025 annual return lists 2,270 storm overflows run by United Utilities in England. 2,270 have a usable spill count. Together they recorded 60,843 spills and 327,453 hours of discharge. The median outlet recorded 15 spills and 29.1 hours.

For a fair comparison with 2024, we use only the 1,917 outlets with a count in both years and a monitor that worked at least 90% of each year. Their spills went from 69,803 to 53,846, a fall of 23%. 1,255 recorded fewer spills and 455 recorded more.

295 outlets (13%) recorded no spills in 2025. 321 (14.1%) recorded 60 or more.

United Utilities’s median of 15 spills per outlet is the 3rd highest of the 10 companies in the return. The England median is 11.

194 outlets had a monitor that worked for less than 90% of the year. Counts from those outlets may be low.

2,270
Outlets listed: 60,843
Spills in 2025: 15
Median per outlet: 327,453
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: 295 13%
1 to 9: 649 28.6%
10 to 19: 297 13.1%
20 to 39: 431 19%
40 to 59: 277 12.2%
60 or more: 321 14.1%

Spills over time

The median outlet run by United Utilities recorded 15 spills in 2025, against 11 across England.

1,917 outlets have a comparable count for both 2024 and 2025, with the monitor working at least 90% of each year. 455 recorded more spills, 1,255 fewer and 207 the same. Together they went from 69,803 to 53,846 spills, a fall of 23%.

Largest rises from 2024 to 2025

Crosby Garret WwTW24 → 159
Laburnham Grove4 → 102
Wray Wastewater Treatment Works (WRAYZ) (017270020)39 → 90

Year	Outlets with a count	Total spills	Median per outlet	England median
2025	2,270	60,843	15	11
2024	2,242	77,813	21	19

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.

Cartmel In Cark Pumping Station (Site ID CARTC) (LAK0099)236 → 30
KIRK BAMPTON WwTW204 → 29
Ireby WwTW164 → 0
MOSSLEY WwTW211 → 48
Strangeways No1 Ww Ntwk PS141 → 0
Marsh Lane CSO137 → 0
Royal Oak CSO159 → 25
Cocklakes WwTW134 → 6
Longsight Park CSO117 → 0
Park Hall Road combined sewer overflow (CHR0012a)117 → 0

Most spills in 2025

1
Lock Lane CSO
Manchester Ship Canal
217spills
2
Blennerhassett Ww PS
River Ellen
172spills
3
BRAYSTONES WwTW
Irish Sea
168spills
4
STAVELEY WwTW
River Kent
167spills
5
North Wirral WwTW (Meols)
River Birket
164spills
5
Plumbland WwTW
River Ellen
164spills
5
Wallasey PS
River Mersey Estuary
164spills
8
GREAT BROUGHTON WwTW
River Derwent
161spills
9
Crosby Garret WwTW
Crosby Garrett Beck
159spills
10
PICA WwTW
Dyan Beck
152spills

Most hours in 2025

1
STAVELEY WwTW
River Kent
3,395hours
2
Gleaston Castle CSO
Gleaston Beck
3,206hours
3
PICA WwTW
Dyan Beck
2,589hours
4
Blennerhassett Ww PS
River Ellen
2,508hours
5
INGLETON WwTW
River Greta
2,446hours
6
OVER KELLET WwTW
Tributary River Keer
2,402hours
7
COCKERMOUTH WwTW
River Derwent
2,354hours
8
BARTON WwTW
Barton Brook
2,207hours
9
Kirkby Stephen WwTW
River Eden
2,170hours
10
EMBLETON WwTW
Tributary Dubwath Beck
2,044hours

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
MERSEY - Transitional	69	2,142	31
Mersey (upstream of Manchester Ship Canal)	51	1,711	33.5
Tame (Swineshaw Brook to Mersey)	47	1,480	31.5
Irwell (Croal to Irk)	56	1,216	21.7
Middle Brook	46	1,081	23.5
Calder - Pendle Water to conf Ribble	28	1,032	36.9
Derwent - conf Cocker to tidal	14	984	70.3
Eden - Eamont to tidal	27	893	33.1
Ellen (lower)	12	890	74.2
The Birket including Arrowe Brook and Fender	38	813	21.4

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