Storm overflow register · South West Water

Ernesettle sewage works: storm overflow spills 2025

Ernesettle sewage treatment works, run by South West Water, has 2 monitored storm overflows discharging to River Tamar (E). In 2025 they recorded 161 spills totalling 1,976 hours, against 134 spills and 1,552 hours in 2024. By hours spilling, it ranks 40 of 334 South West Water works, where 1 spilled longest.

Works size: 63,952 population equivalent (ERNESETTLE AND SALTASH 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.

JanFebMarAprMayJunJulAugSepOctNovDecErnesettle Sewage…1 Jan 2025 13:34 GMT, 1 min73 spills, 71.8 h, 4 Jan to 8 Jan12 spills, 6.6 h, 23 Jan to 24 Jan65 spills, 59.7 h, 26 Jan to 30 Jan2 spills, 3 h, 19 Feb to 19 Feb7 spills, 1.1 h, 21 Feb to 21 Feb104 spills, 103.2 h, 23 Feb to 28 Feb21 Mar 2025 19:56 GMT, 4 min48 spills, 13.2 h, 15 Apr to 16 Apr123 spills, 44.5 h, 18 Apr to 20 Apr15 spills, 4.3 h, 22 Apr to 23 Apr2 spills, 0 h, 25 Apr to 25 Apr7 spills, 0.2 h, 5 Jun to 5 Jun6 spills, 2 h, 7 Jun to 7 Jun82 spills, 26.5 h, 12 Jun to 14 Jun7 spills, 1.8 h, 19 Jul to 20 Jul27 Aug 2025 08:15 GMT, 65 min12 spills, 6.1 h, 28 Aug to 29 Aug7 spills, 6.9 h, 30 Aug to 31 Aug3 spills, 1.7 h, 1 Sep to 1 Sep95 spills, 48.6 h, 2 Sep to 5 Sep48 spills, 11.3 h, 9 Sep to 13 Sep77 spills, 12.5 h, 14 Sep to 15 Sep5 spills, 1.6 h, 17 Sep to 17 Sep18 Sep 2025 08:05 GMT, 3 min10 spills, 1.2 h, 20 Sep to 20 Sep5 spills, 0.3 h, 25 Sep to 26 Sep196 spills, 22.7 h, 2 Oct to 4 Oct6 Oct 2025 13:57 GMT, 3 min28 spills, 12 h, 19 Oct to 20 Oct37 spills, 8.1 h, 22 Oct to 24 Oct2 spills, 0.1 h, 30 Oct to 30 Oct167 spills, 25.5 h, 4 Nov to 7 Nov194 spills, 164.1 h, 8 Nov to 17 Nov2 spills, 0 h, 18 Nov to 18 Nov143 spills, 19.8 h, 22 Nov to 24 Nov27 Nov 2025 21:41 GMT, 2 min75 spills, 308.8 h, 29 Nov to 14 Dec15 spills, 197.6 h, 15 Dec to 23 Dec24 Dec 2025 10:56 GMT, 5 minErnesettle Sewage…29 Jan 2025 14:39 GMT, 8.2 h2 spills, 85.3 h, 23 Feb to 27 Feb15 Apr 2025 14:21 GMT, 6.2 h18 Apr 2025 15:14 GMT, 34.7 h12 Jun 2025 11:30 GMT, 9.8 h13 Jun 2025 18:15 GMT, 9.5 h29 Aug 2025 01:29 GMT, 2.2 h2 spills, 41 h, 3 Sep to 4 Sep2 spills, 6.9 h, 3 Oct to 4 Oct2 spills, 5.7 h, 4 Nov to 5 Nov2 spills, 153.2 h, 9 Nov to 16 Nov3 spills, 268.5 h, 1 Dec to 13 Dec3 spills, 159.5 h, 15 Dec to 22 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.

01M2M3MJan 2025: 146 h spilling ≈ 160,313 m³ (range 63,856-402,472 m³)JanFeb 2025: 193 h spilling ≈ 211,047 m³ (range 84,065-529,843 m³)FebMar 2025: 0.1 h spilling ≈ 110 m³ (range 44-275 m³)MarApr 2025: 103 h spilling ≈ 112,646 m³ (range 44,869-282,803 m³)AprMay 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)MayJun 2025: 48 h spilling ≈ 52,378 m³ (range 20,863-131,498 m³)JunJul 2025: 1.8 h spilling ≈ 1,972 m³ (range 786-4,952 m³)JulAug 2025: 16 h spilling ≈ 17,861 m³ (range 7,115-44,841 m³)AugSep 2025: 118 h spilling ≈ 129,521 m³ (range 51,591-325,168 m³)SepOct 2025: 50 h spilling ≈ 54,570 m³ (range 21,736-137,000 m³)OctNov 2025: 377 h spilling ≈ 413,000 m³ (range 164,506-1.0 million m³)NovDec 2025: 926 h spilling ≈ 1.0 million m³ (range 404,043-2.5 million m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
15 Dec 2025, 01:08Ernesettle Sewage Treatment Works8.0 days83,512 - 526,358 m³
5 Dec 2025, 10:26Ernesettle Sewage Treatment Works8.0 days83,279 - 524,891 m³
5 Dec 2025, 12:30Ernesettle Sewage Treatment Works6.5 days67,857 - 427,689 m³
15 Dec 2025, 05:38Ernesettle Sewage Treatment Works5.9 days62,256 - 392,385 m³
11 Nov 2025, 06:47Ernesettle Sewage Treatment Works4.8 days50,151 - 316,090 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 estimate2.2 million m³range 862,339 - 5.4 million m³
In litres2.2 billionrange 862.3 million - 5.4 billion L
Olympic swimming pools866at 2,500 m³ each
Organic load, as people's raw sewage3.2 millionperson-days of untreated BOD

Assumed spill rate while spilling: 121.2 - 764.2 L/s (central 304.4 L/s), from a dry-weather flow of 121.2 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 34,494 kg194,844 kg1.1 million kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 90,546 kg920,097 kg3.9 million kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 1,638 kg13,639 kg50,547 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 1,035 kg5,629 kg29,350 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 86.2 trillion organisms2.2 × 10¹⁵ organisms5.4 × 10¹⁶ 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.

Ernesettle Sewage Treatment Works

Inlet overflow at sewage works · discharges to River Tamar (E)

Spills 2025
114 (1,185 hours) · up 34% on 2024
Spills 2024
85 (712 hours)
Long-term average
73.2 spills a year (monitored since 2016)
Monitor uptime
95% of the year
High-spill reason (company)
Performance - SW Infiltration
Investigation
Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Not part of a WFD catchment
Outlet location
SX44246023 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00419 · 301142 · company name: ERNESETTLE STW_SO_PLYMOUTH

Ernesettle Sewage Treatment Works

Storm tank at sewage works · discharges to River Tamar (E)

Spills 2025
47 (791 hours) · down 4% on 2024
Spills 2024
49 (840 hours)
Long-term average
61.1 spills a year (monitored since 2016)
Monitor uptime
89% of the year · Sensor failure / issue
High-spill reason (company)
Performance - SW Infiltration
Investigation
No investigation activity in reporting period
Improvement
No improvement action in reporting period
WFD catchment
Not part of a WFD catchment
Outlet location
SX44246023 (OS grid reference) · View on Apple Maps
EA ID / permit
SBB00420 · 301142 · company name: ERNESETTLE STW_SSO_PLYMOUTH

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.