Storm overflow register · Anglian Water

Cromer sewage works: storm overflow spills 2025

Cromer sewage treatment works, run by Anglian Water, has 1 monitored storm overflow discharging to The North Sea. In 2025 it recorded 72 spills totalling 272 hours, against 91 spills and 524 hours in 2024. By hours spilling, it ranks 81 of 419 Anglian Water works, where 1 spilled longest.

Works size: 31,569 population equivalent (CROMER 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.

JanFebMarAprMayJunJulAugSepOctNovDecCromer Water…2 spills, 4.2 h, 1 Jan to 1 Jan2 spills, 1.3 h, 2 Jan to 2 Jan17 spills, 19.8 h, 5 Jan to 6 Jan2 spills, 0.9 h, 22 Jan to 22 Jan5 spills, 3.6 h, 23 Jan to 24 Jan3 spills, 8.5 h, 26 Jan to 27 Jan2 spills, 10.8 h, 28 Jan to 29 Jan2 spills, 1.6 h, 10 Feb to 10 Feb19 Feb 2025 13:16 GMT, 54 min22 Feb 2025 04:16 GMT, 108 min2 spills, 3.2 h, 24 Feb to 24 Feb26 Feb 2025 12:08 GMT, 11.6 h13 Apr 2025 18:46 GMT, 38 min15 Apr 2025 08:34 GMT, 7 h2 spills, 0.9 h, 24 May to 24 May7 spills, 19.6 h, 27 May to 28 May6 Jun 2025 10:12 GMT, 76 min2 spills, 1.3 h, 7 Jun to 7 Jun14 Jun 2025 00:16 GMT, 12 h4 spills, 0.9 h, 6 Jul to 6 Jul2 spills, 1.7 h, 7 Jul to 7 Jul5 spills, 21.4 h, 19 Jul to 21 Jul24 Jul 2025 06:50 GMT, 6.4 h26 Jul 2025 14:50 GMT, 2.2 h4 Aug 2025 16:04 GMT, 2.2 h5 spills, 12.3 h, 29 Aug to 30 Aug2 spills, 0.9 h, 1 Sep to 1 Sep6 spills, 2.3 h, 3 Sep to 3 Sep2 spills, 1.3 h, 10 Sep to 10 Sep13 Sep 2025 16:44 GMT, 114 min2 spills, 5.8 h, 14 Sep to 14 Sep4 spills, 6.9 h, 17 Sep to 17 Sep21 Sep 2025 02:20 GMT, 6 min23 Sep 2025 06:52 GMT, 8 min8 spills, 4 h, 3 Oct to 4 Oct2 spills, 1.7 h, 20 Oct to 20 Oct3 spills, 6.2 h, 22 Oct to 23 Oct25 Oct 2025 04:10 GMT, 2.7 h2 spills, 1.7 h, 1 Nov to 1 Nov3 spills, 2.5 h, 10 Nov to 10 Nov25 spills, 25.1 h, 14 Nov to 15 Nov15 spills, 7.3 h, 19 Nov to 21 Nov4 spills, 16.5 h, 22 Nov to 23 Nov24 Nov 2025 18:34 GMT, 18 min29 Nov 2025 15:42 GMT, 6 min4 spills, 1.4 h, 1 Dec to 1 Dec3 spills, 5.8 h, 5 Dec to 6 Dec4 spills, 1.6 h, 7 Dec to 7 Dec9 Dec 2025 04:02 GMT, 8.3 h2 spills, 0.8 h, 16 Dec to 16 Dec4 spills, 8.4 h, 18 Dec to 18 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.

020k40k60k80kJan 2025: 49 h spilling ≈ 26,559 m³ (range 10,579-66,677 m³)JanFeb 2025: 19 h spilling ≈ 10,332 m³ (range 4,115-25,938 m³)FebMar 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MarApr 2025: 7.6 h spilling ≈ 4,111 m³ (range 1,637-10,321 m³)AprMay 2025: 21 h spilling ≈ 11,089 m³ (range 4,417-27,839 m³)MayJun 2025: 15 h spilling ≈ 7,897 m³ (range 3,146-19,827 m³)JunJul 2025: 33 h spilling ≈ 17,634 m³ (range 7,024-44,271 m³)JulAug 2025: 15 h spilling ≈ 7,843 m³ (range 3,124-19,691 m³)AugSep 2025: 19 h spilling ≈ 10,440 m³ (range 4,158-26,209 m³)SepOct 2025: 15 h spilling ≈ 7,951 m³ (range 3,167-19,962 m³)OctNov 2025: 54 h spilling ≈ 28,993 m³ (range 11,549-72,788 m³)NovDec 2025: 26 h spilling ≈ 14,280 m³ (range 5,688-35,851 m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
21 Jul 2025, 09:24Cromer Water Recycling Centre12.4 h2,665 - 16,794 m³
14 Jun 2025, 00:16Cromer Water Recycling Centre12.0 h2,593 - 16,341 m³
26 Feb 2025, 12:08Cromer Water Recycling Centre11.6 h2,506 - 15,798 m³
28 May 2025, 00:00Cromer Water Recycling Centre11.6 h2,492 - 15,707 m³
15 Nov 2025, 00:00Cromer Water Recycling Centre9.7 h2,083 - 13,127 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 estimate147,183 m³range 58,626 - 369,510 m³
In litres147.2 millionrange 58.6 million - 369.5 million L
Olympic swimming pools59at 2,500 m³ each
Organic load, as people's raw sewage220,775person-days of untreated BOD

Assumed spill rate while spilling: 59.8 - 377.2 L/s (central 150.3 L/s), from a dry-weather flow of 59.8 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 2,345 kg13,247 kg73,902 kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 6,156 kg62,553 kg266,417 kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 111 kg927 kg3,436 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 70 kg383 kg1,995 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 5.9 trillion organisms147.2 trillion organisms3.7 × 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.

Cromer Water Recycling Centre

Inlet overflow at sewage works · discharges to The North Sea

Spills 2025
72 (272 hours) · down 21% on 2024
Spills 2024
91 (524 hours)
Long-term average
134.1 spills a year (monitored since 2019)
Monitor uptime
100% of the year
High-spill reason (company)
Not Applicable - Ongoing investigation
Investigation
Env Act (SODRP) investigation ongoing
Improvement
No improvement action in reporting period
WFD catchment
Norfolk East (GB650503520003)
Outlet location
TG1883045510 (OS grid reference) · View on Apple Maps
EA ID / permit
AWS00299 · AEECS12415 · company name: Cromer STW

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.