Storm overflow register · Anglian Water

Tilbury sewage works: storm overflow spills 2025

Tilbury sewage treatment works, run by Anglian Water, has 1 monitored storm overflow discharging to Ouse (Newport Pagnell to Roxton). In 2025 it recorded 64 spills totalling 142 hours, against 56 spills and 162 hours in 2024. By hours spilling, it ranks 140 of 419 Anglian 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.

JanFebMarAprMayJunJulAugSepOctNovDecTilbury Water…13 spills, 4.8 h, 1 Jan to 1 Jan55 spills, 18.4 h, 5 Jan to 6 Jan7 spills, 1.5 h, 8 Jan to 8 Jan22 Jan 2025 02:00 GMT, 2 min33 spills, 5.8 h, 26 Jan to 27 Jan26 spills, 7.2 h, 28 Jan to 28 Jan9 spills, 1.3 h, 31 Jan to 31 Jan7 spills, 1.2 h, 7 Feb to 7 Feb10 Feb 2025 20:46 GMT, 4 min4 spills, 0.4 h, 22 Feb to 22 Feb25 spills, 3.6 h, 24 Feb to 24 Feb7 spills, 1.6 h, 26 Feb to 26 Feb4 spills, 0.2 h, 23 Mar to 23 Mar3 spills, 0.1 h, 24 Mar to 24 Mar8 spills, 5.2 h, 15 Apr to 15 Apr8 spills, 0.6 h, 21 Apr to 21 Apr9 spills, 4.6 h, 23 Apr to 23 Apr3 spills, 0.8 h, 24 May to 24 May8 spills, 1.4 h, 27 May to 27 May12 spills, 0.9 h, 5 Jun to 5 Jun4 spills, 2.7 h, 7 Jun to 7 Jun7 spills, 3.7 h, 7 Jul to 7 Jul14 spills, 6 h, 19 Jul to 19 Jul10 spills, 4 h, 21 Jul to 21 Jul14 spills, 0.7 h, 22 Jul to 22 Jul3 spills, 0.1 h, 24 Jul to 24 Jul31 Jul 2025 12:44 GMT, 2.6 h3 spills, 0.1 h, 8 Aug to 8 Aug3 spills, 2.6 h, 29 Aug to 29 Aug2 spills, 0.1 h, 1 Sep to 1 Sep13 spills, 4.5 h, 3 Sep to 4 Sep2 spills, 0.1 h, 10 Sep to 10 Sep2 spills, 0.1 h, 14 Sep to 14 Sep5 spills, 2.2 h, 3 Oct to 4 Oct8 spills, 4.3 h, 20 Oct to 20 Oct6 spills, 7.4 h, 22 Oct to 23 Oct15 spills, 8.2 h, 29 Oct to 29 Oct2 spills, 0.1 h, 31 Oct to 31 Oct26 spills, 2.3 h, 1 Nov to 2 Nov6 spills, 2.2 h, 10 Nov to 10 Nov31 spills, 4.5 h, 13 Nov to 14 Nov9 spills, 0.5 h, 19 Nov to 19 Nov28 spills, 4.1 h, 22 Nov to 23 Nov8 spills, 3 h, 2 Dec to 3 Dec7 spills, 2.3 h, 3 Dec to 4 Dec3 spills, 0.2 h, 6 Dec to 6 Dec11 spills, 1.7 h, 7 Dec to 7 Dec9 Dec 2025 08:58 GMT, 2 min18 spills, 7.7 h, 18 Dec to 19 Dec28 spills, 4.4 h, 21 Dec to 22 Dec

Hours spilling by month, 2025

010203040Jan 2025: 39 hours spillingJanFeb 2025: 6.9 hours spillingFebMar 2025: 0.3 hours spillingMarApr 2025: 10 hours spillingAprMay 2025: 2.3 hours spillingMayJun 2025: 3.5 hours spillingJunJul 2025: 17 hours spillingJulAug 2025: 2.7 hours spillingAugSep 2025: 4.7 hours spillingSepOct 2025: 22 hours spillingOctNov 2025: 14 hours spillingNovDec 2025: 19 hours spillingDec
Hours, measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDuration
29 Oct 2025, 13:00Tilbury Water Recycling Centre7.1 h
18 Dec 2025, 13:16Tilbury Water Recycling Centre6.5 h
23 Oct 2025, 00:00Tilbury Water Recycling Centre4.3 h
23 Apr 2025, 05:48Tilbury Water Recycling Centre4.2 h
5 Jan 2025, 09:56Tilbury Water Recycling Centre4.0 h

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 estimate2,433 m³range 969 - 6,108 m³
In litres2.4 millionrange 969,150 - 6.1 million L
Olympic swimming pools1.0at 2,500 m³ each
Organic load, as people's raw sewage3,650person-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) 39 kg219 kg1,222 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 102 kg1,034 kg4,404 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 1.8 kg15 kg57 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 1.2 kg6.3 kg33 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 96.9 billion organisms2.4 trillion organisms61.1 trillion 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.

Tilbury Water Recycling Centre

Inlet overflow at sewage works · discharges to Ouse (Newport Pagnell to Roxton)

Spills 2025
64 (142 hours) · up 14% on 2024
Spills 2024
56 (162 hours)
Long-term average
60.0 spills a year (monitored since 2024)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - Hydraulic capacity
Investigation
Env Act (SODRP) investigation ongoing, Bathing Water and/or Shellfish Water investigation ongoing
Improvement
No improvement action in reporting period
WFD catchment
THAMES MIDDLE (GB530603911402)
Outlet location
TQ6565075310 (OS grid reference) · View on Apple Maps
EA ID / permit
AWS01383 · CNTW.0532 · company name: Tilbury Water Recycling Centre

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 Anglian 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.