Storm overflow register · South West Water

Lutton sewage works: storm overflow spills 2025

Lutton sewage treatment works, run by South West Water, has 2 monitored storm overflows discharging to (S) River Piall, (S)River Piall. In 2025 they recorded 224 spills totalling 2,894 hours, against 228 spills and 2,820 hours in 2024. By hours spilling, it ranks 12 of 334 South West Water works, where 1 spilled longest.

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.

JanFebMarAprMayJunJulAugSepOctNovDecLutton STW1 Jan 2025 16:40 GMT, 94 min2 spills, 150.6 h, 4 Jan to 11 Jan2 spills, 8.8 h, 24 Jan to 24 Jan26 Jan 2025 14:59 GMT, 127.4 h19 Feb 2025 19:56 GMT, 5.6 h21 Feb 2025 11:17 GMT, 3.5 h23 Feb 2025 11:18 GMT, 131 h3 spills, 9.7 h, 15 Apr to 16 Apr18 Apr 2025 05:50 GMT, 49 h22 Apr 2025 20:15 GMT, 11.5 h2 spills, 1.2 h, 7 Jun to 7 Jun12 Jun 2025 07:56 GMT, 6.6 h13 Jun 2025 15:40 GMT, 55.2 h27 Aug 2025 09:31 GMT, 24 min28 Aug 2025 23:00 GMT, 3.8 h5 spills, 9 h, 30 Aug to 1 Sep9 spills, 61.7 h, 2 Sep to 5 Sep3 spills, 38.1 h, 9 Sep to 11 Sep3 spills, 7.9 h, 13 Sep to 13 Sep2 spills, 34.8 h, 14 Sep to 15 Sep3 spills, 84.7 h, 17 Sep to 20 Sep4 spills, 16.5 h, 3 Oct to 4 Oct2 spills, 18.4 h, 19 Oct to 20 Oct4 spills, 19.4 h, 22 Oct to 23 Oct30 Oct 2025 22:28 GMT, 17 min4 spills, 12.5 h, 31 Oct to 2 Nov3 spills, 77 h, 4 Nov to 8 Nov4 spills, 213.1 h, 9 Nov to 19 Nov8 spills, 794.6 h, 22 Nov to 26 DecLutton STW66 spills, 78.4 h, 4 Jan to 9 Jan11 Jan 2025 05:19 GMT, 2 min2 spills, 0.1 h, 12 Jan to 12 Jan15 spills, 12.4 h, 23 Jan to 24 Jan108 spills, 43.2 h, 25 Jan to 30 Jan3 spills, 1.5 h, 31 Jan to 31 Jan11 spills, 1.8 h, 19 Feb to 20 Feb2 spills, 0.6 h, 21 Feb to 21 Feb89 spills, 56.2 h, 23 Feb to 27 Feb4 spills, 9.2 h, 15 Apr to 16 Apr27 spills, 15 h, 18 Apr to 19 Apr2 spills, 5.1 h, 22 Apr to 23 Apr2 spills, 0.4 h, 11 May to 11 May2 spills, 0.5 h, 27 May to 27 May5 spills, 1 h, 7 Jun to 7 Jun5 spills, 5.3 h, 12 Jun to 12 Jun12 spills, 23.2 h, 13 Jun to 14 Jun3 spills, 0.2 h, 19 Jul to 19 Jul5 spills, 0.4 h, 27 Aug to 27 Aug3 spills, 4.2 h, 28 Aug to 29 Aug10 spills, 8.2 h, 30 Aug to 1 Sep24 spills, 19.3 h, 2 Sep to 4 Sep14 spills, 5.3 h, 9 Sep to 10 Sep4 spills, 0.1 h, 11 Sep to 11 Sep8 spills, 1.6 h, 12 Sep to 13 Sep11 spills, 6 h, 14 Sep to 14 Sep52 spills, 15.2 h, 17 Sep to 18 Sep4 spills, 0.5 h, 20 Sep to 20 Sep27 Sep 2025 23:16 GMT, 3 min17 spills, 6.9 h, 2 Oct to 4 Oct3 spills, 0.4 h, 8 Oct to 8 Oct10 spills, 8 h, 19 Oct to 20 Oct12 spills, 2.7 h, 22 Oct to 23 Oct3 spills, 0.6 h, 30 Oct to 30 Oct10 spills, 3.4 h, 31 Oct to 2 Nov12 spills, 11 h, 4 Nov to 5 Nov3 spills, 2.5 h, 7 Nov to 7 Nov77 spills, 165 h, 9 Nov to 16 Nov18 Nov 2025 10:08 GMT, 13 min21 spills, 8.6 h, 22 Nov to 24 Nov10 spills, 3.3 h, 26 Nov to 27 Nov132 spills, 258 h, 28 Nov to 12 Dec76 spills, 155.2 h, 15 Dec to 22 Dec

Hours spilling by month, 2025

05001,0001,500Jan 2025: 424 hours spillingJanFeb 2025: 199 hours spillingFebMar 2025: 0.0 hours spillingMarApr 2025: 100 hours spillingAprMay 2025: 0.9 hours spillingMayJun 2025: 93 hours spillingJunJul 2025: 0.2 hours spillingJulAug 2025: 22 hours spillingAugSep 2025: 279 hours spillingSepOct 2025: 79 hours spillingOctNov 2025: 685 hours spillingNovDec 2025: 1,013 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
27 Nov 2025, 06:55Lutton STW28.9 days
9 Nov 2025, 13:10Lutton STW8.5 days
23 Feb 2025, 11:18Lutton STW5.5 days
26 Jan 2025, 14:59Lutton STW5.3 days
7 Jan 2025, 15:46Lutton STW3.5 days

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.

This works serves fewer than 2,000 people, or was not matched to a UWWTD report, so its size is not published. The population equivalent above is a placeholder of 1,000. Enter the population served if you know it.

Volume, central estimate49,590 m³range 19,753 - 124,499 m³
In litres49.6 millionrange 19.8 million - 124.5 million L
Olympic swimming pools20at 2,500 m³ each
Organic load, as people's raw sewage74,386person-days of untreated BOD

Assumed spill rate while spilling: 1.9 - 11.9 L/s (central 4.8 L/s), from a dry-weather flow of 1.9 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 790 kg4,463 kg24,900 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 2,074 kg21,076 kg89,764 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 38 kg312 kg1,158 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 24 kg129 kg672 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 2.0 trillion organisms49.6 trillion organisms1.2 × 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.

Lutton STW

Storm tank at sewage works · discharges to (S) River Piall

Spills 2025
118 (1,954 hours) · no change on 2024
Spills 2024
118 (2,074 hours)
Long-term average
81.4 spills a year (monitored since 2021)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
UWWTR investigation ongoing, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Piall (GB108047004020)
Outlet location
SX59875917 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00724 · 033125/SS/01 · company name: LUTTON STW_SSO_LUTTON

Lutton STW

Inlet overflow at sewage works · discharges to (S)River Piall

Spills 2025
106 (940 hours) · down 4% on 2024
Spills 2024
110 (746 hours)
Long-term average
74.4 spills a year (monitored since 2021)
Monitor uptime
100% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Piall (GB108047004020)
Outlet location
SX59875917 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00723 · 033125/SF/01 · company name: LUTTON STW_SO_LUTTON

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 South West Water 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.