Storm overflow register · United Utilities

Braystones sewage works: storm overflow spills 2025

Braystones sewage treatment works, run by United Utilities, has 1 monitored storm overflow discharging to Irish Sea. In 2025 it recorded 168 spills totalling 1,082 hours, against 163 spills and 511 hours in 2024. By hours spilling, it ranks 40 of 289 United Utilities works, where 1 spilled longest.

Works size: 10,787 population equivalent (BRAYSTONES STW, UWWTD 2018). Used for the spill volume estimate.

Every spill in 2025

Each blue mark is one spill, placed by when it started and sized by how long it lasted. Hover over a mark for the date and duration.

JanFebMarAprMayJunJulAugSepOctNovDecBraystones WwTW18 spills, 4.2 h, 1 Jan to 1 Jan43 spills, 10 h, 5 Jan to 7 Jan4 spills, 0.6 h, 13 Jan to 13 Jan4 spills, 1 h, 21 Jan to 21 Jan36 spills, 10.3 h, 23 Jan to 24 Jan45 spills, 6.8 h, 26 Jan to 28 Jan8 spills, 2.1 h, 31 Jan to 31 Jan2 Feb 2025 11:52 GMT, 7 min10 spills, 2.7 h, 4 Feb to 4 Feb14 spills, 3 h, 19 Feb to 20 Feb32 spills, 7.7 h, 21 Feb to 22 Feb66 spills, 11.2 h, 23 Feb to 24 Feb22 spills, 3.1 h, 26 Feb to 26 Feb5 spills, 0.7 h, 6 Mar to 6 Mar4 spills, 0.5 h, 22 Mar to 22 Mar3 spills, 0.8 h, 27 Mar to 27 Mar6 spills, 1.6 h, 29 Mar to 29 Mar17 spills, 4.3 h, 14 Apr to 14 Apr2 spills, 0.4 h, 16 Apr to 16 Apr17 Apr 2025 11:32 GMT, 12 min2 spills, 0.4 h, 18 Apr to 18 Apr9 spills, 3 h, 23 May to 24 May25 May 2025 17:44 GMT, 12 min25 spills, 8.6 h, 29 May to 30 May27 spills, 7.2 h, 3 Jun to 3 Jun2 spills, 0.3 h, 4 Jun to 4 Jun5 spills, 4.2 h, 6 Jun to 6 Jun11 spills, 9 h, 9 Jun to 10 Jun4 spills, 1.8 h, 12 Jun to 12 Jun15 spills, 11.3 h, 14 Jun to 14 Jun9 spills, 3.9 h, 21 Jun to 22 Jun6 spills, 3.3 h, 24 Jun to 24 Jun16 spills, 5.6 h, 25 Jun to 26 Jun4 spills, 0.5 h, 27 Jun to 27 Jun43 spills, 7.1 h, 4 Jul to 5 Jul14 Jul 2025 03:24 GMT, 8 min46 spills, 7.1 h, 15 Jul to 16 Jul7 spills, 0.7 h, 20 Jul to 21 Jul36 spills, 11.6 h, 3 Aug to 5 Aug14 Aug 2025 10:11 GMT, 2.4 h15 spills, 2.3 h, 28 Aug to 28 Aug4 spills, 0.6 h, 29 Aug to 29 Aug2 spills, 0.3 h, 30 Aug to 30 Aug13 spills, 4.7 h, 1 Sep to 1 Sep11 spills, 5 h, 2 Sep to 3 Sep2 spills, 0.3 h, 4 Sep to 4 Sep4 spills, 0.5 h, 7 Sep to 7 Sep3 spills, 0.4 h, 8 Sep to 8 Sep10 spills, 1.4 h, 10 Sep to 11 Sep18 spills, 2.6 h, 12 Sep to 13 Sep53 spills, 10.2 h, 14 Sep to 17 Sep118 spills, 53.1 h, 19 Sep to 24 Sep4 spills, 0.5 h, 25 Sep to 25 Sep9 spills, 1.2 h, 27 Sep to 28 Sep266 spills, 72.4 h, 30 Sep to 9 Oct3 spills, 0.4 h, 19 Oct to 19 Oct15 spills, 8.2 h, 24 Oct to 25 Oct9 spills, 3.5 h, 26 Oct to 26 Oct6 spills, 5.3 h, 27 Oct to 28 Oct4 spills, 1.6 h, 29 Oct to 29 Oct2157 spills, 748.2 h, 31 Oct to 31 Dec

Estimated spill volume by month, 2025

Hours spilling each month × the estimated spill rate for a works of this size. The bars are central estimates and the whiskers show the low-high range. Method.

050k100k150k200kJan 2025: 35 h spilling ≈ 6,469 m³ (range 2,577-16,241 m³)JanFeb 2025: 28 h spilling ≈ 5,138 m³ (range 2,047-12,900 m³)FebMar 2025: 3.5 h spilling ≈ 647 m³ (range 258-1,624 m³)MarApr 2025: 5.3 h spilling ≈ 980 m³ (range 390-2,459 m³)AprMay 2025: 12 h spilling ≈ 2,163 m³ (range 861-5,429 m³)MayJun 2025: 47 h spilling ≈ 8,668 m³ (range 3,453-21,763 m³)JunJul 2025: 15 h spilling ≈ 2,754 m³ (range 1,097-6,914 m³)JulAug 2025: 17 h spilling ≈ 3,179 m³ (range 1,266-7,981 m³)AugSep 2025: 80 h spilling ≈ 14,786 m³ (range 5,890-37,122 m³)SepOct 2025: 93 h spilling ≈ 17,189 m³ (range 6,847-43,154 m³)OctNov 2025: 347 h spilling ≈ 64,117 m³ (range 25,539-160,969 m³)NovDec 2025: 399 h spilling ≈ 73,821 m³ (range 29,404-185,330 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
5 Nov 2025, 15:00Braystones WwTW1.0 days1,769 - 11,152 m³
7 Dec 2025, 17:33Braystones WwTW1.0 days1,767 - 11,136 m³
18 Dec 2025, 01:05Braystones WwTW22.6 h1,661 - 10,471 m³
17 Dec 2025, 05:38Braystones WwTW19.5 h1,432 - 9,025 m³
14 Dec 2025, 12:37Braystones WwTW18.9 h1,389 - 8,755 m³

Estimated 2025 spill volume and pollution

Estimate, not a measurement. Monitors record how long an overflow spills, not how much. This calculator back-calculates a spill rate from the size of the works, using the Environment Agency's permit formulae, and multiplies it by published storm-sewage concentrations. How it works.

Volume, central estimate200,041 m³range 79,680 - 502,210 m³
In litres200.0 millionrange 79.7 million - 502.2 million L
Olympic swimming pools80at 2,500 m³ each
Organic load, as people's raw sewage300,061person-days of untreated BOD

Assumed spill rate while spilling: 20.5 - 128.9 L/s (central 51.3 L/s), from a dry-weather flow of 20.5 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 3,187 kg18,004 kg100,442 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 8,366 kg85,017 kg362,093 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 151 kg1,260 kg4,671 kg 1.9 / 6.3 / 9.3 mg/L
Low: Germany, Brombach 2005; typical/high: Paris range 3.3-9.3 midpoint and top, Gasperi 2012 (via botturi); no UK value found
Total phosphorus 96 kg520 kg2,712 kg 1.2 / 2.6 / 5.4 mg/L
Low/high: Paris, Gasperi 2012; typical: Slovakia (via botturi). UK figure of 10 mg/L treated as an outlier
E. coli 8.0 trillion organisms200.0 trillion organisms5.0 × 10¹⁵ organisms 10,000 / 100,000 / 1.0 million per 100 mL
Median range at CSO and retention-tank outlets, Stott et al. 2018 (via botturi); typical = log midpoint

Low combines the low spill rate with low concentrations, and high combines high with high, so the true figure is very likely inside the range. Long spills become more diluted as they go on, so the central figure tends to overstate the load of long events. The calculator does not estimate the effect on the receiving water, which depends on river flow or tide at the time of the spill.

Braystones WwTW

Inlet overflow at sewage works · discharges to Irish Sea

Spills 2025
168 (1,082 hours) · up 3% on 2024
Spills 2024
163 (511 hours)
Long-term average
164.4 spills a year (monitored since 2017)
Monitor uptime
100% of the year
High-spill reason (company)
Data collection - Confirmed exceptional weather
Investigation
No investigation activity in reporting period
Improvement
No improvement action in reporting period
Bathing water
Seascale
WFD catchment
Ehen (lower) (GB112074069980)
Outlet location
NY0076005070 (OS grid reference) · View on Apple Maps
EA ID / permit
UUP00306 · 017470152 · company name: BRAYSTONES WwTW

How the estimate works

  1. Dry-weather flow (DWF) = population × water use per person × (1 + infiltration). Water use is 136.5 L per person per day, England's per-capita consumption for 2024-25 [EA]. Infiltration of groundwater into sewers is taken as 0-40% of that flow [Escritt, via HBF]. The Environment Agency defines DWF as PG + I + E [EA].
  2. Population. The size of each works comes from the load entering it as reported under the Urban Waste Water Treatment Directive, in population equivalents (1 p.e. = 60 g of BOD a day) [UWWTD]. We treat population equivalent as population. That overstates flow where trade effluent adds load, and no official source links the two. Works serving fewer than 2,000 p.e. are not reported, so their size has to be entered by hand.
  3. Low spill rate = DWF. This is the method used by Giakoumis & Voulvoulis (2026), which they note likely underestimates storm loads [G&V].
  4. High spill rate = Formula A − flow to full treatment = (DWF + 1360P) − 3DWF. This is the largest flow the permit expects the storm tanks to handle before it passes on to treatment or overflows [EA]. The central rate is the geometric mean of the low and high rates.
  5. Volume = spill rate × hours spilling, with hours taken from the event duration monitor.
  6. Pollution = volume × published storm-sewage concentrations [Botturi et al.] [US EPA]. Organic load is also shown as person-days of untreated sewage at 60 g of BOD per person per day [UWWTD].

What this cannot tell you. It gives no real flow for any single spill, and no effect on the river or sea, which depends on the flow, tide and the other pressures on the water at the time. It gives no figure for spills from overflows on the sewer network, which serve catchments of unknown size. It is a way to put hours into rough physical terms, not a substitute for flow monitoring.

Sources

  1. EA: Water companies - environmental permits for storm overflows and emergency overflows
  2. EA: Water resources 2024 to 2025 - per capita consumption
  3. HBF: Foul sewer design - historic conventions (citing Escritt 1984 on infiltration)
  4. Giakoumis & Voulvoulis (2026), Environ. Sci.: Water Res. Technol., doi:10.1039/D5EW00860C
  5. Botturi et al. (2021), Crit. Rev. Environ. Sci. Technol. 51:1585 - CSO quality review, Table 2
  6. US EPA (2004) Report to Congress on CSOs and SSOs, chapter 4
  7. Urban Waste Water Treatment Directive, Article 2(6): 1 p.e. = 60 g BOD5/day
  8. Olympic-size swimming pool: 2,500 m³ at the nominal 2 m depth

← All United Utilities works · Contains Environment Agency data licensed under the Open Government Licence v3.0. Spill start and stop times: © Environment Agency copyright and/or database right 2026. All rights reserved. They are water-company data and have not been verified by the Environment Agency. Works size: EEA Waterbase UWWTD. How to read the data.