Storm overflow register · Yorkshire Water

Huddersfield sewage works: storm overflow spills 2025

Huddersfield sewage treatment works, run by Yorkshire Water, has 4 monitored storm overflows discharging to River Calder & River Colne. In 2025 they recorded 254 spills totalling 1,754 hours, against 355 spills and 3,239 hours in 2024. By hours spilling, it ranks 9 of 283 Yorkshire Water works, where 1 spilled longest.

Works size: 276,920 population equivalent (HUDDERSFIELD 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.

JanFebMarAprMayJunJulAugSepOctNovDecHuddersfield STW98 spills, 173.8 h, 1 Jan to 10 Jan59 spills, 80.3 h, 12 Jan to 18 Jan39 spills, 9.8 h, 19 Jan to 21 Jan24 spills, 15 h, 23 Jan to 25 Jan28 spills, 27.5 h, 26 Jan to 28 Jan2 spills, 4.5 h, 23 Feb to 24 Feb26 Feb 2025 09:30 GMT, 75 min5 spills, 12 h, 22 Mar to 23 Mar3 spills, 1.5 h, 27 May to 27 May6 spills, 3.5 h, 6 Jun to 6 Jun2 spills, 1.5 h, 8 Jun to 8 Jun3 spills, 3.3 h, 10 Jun to 10 Jun6 Jul 2025 21:15 GMT, 5 h15 Jul 2025 21:15 GMT, 2 h19 Jul 2025 16:45 GMT, 60 min2 spills, 2.8 h, 20 Jul to 20 Jul2 spills, 1.3 h, 3 Sep to 4 Sep11 Sep 2025 20:00 GMT, 30 min3 spills, 5.3 h, 15 Sep to 16 Sep3 spills, 5.3 h, 17 Sep to 17 Sep12 spills, 23 h, 20 Sep to 21 Sep28 Sep 2025 01:45 GMT, 2.8 h9 spills, 27.3 h, 3 Oct to 4 Oct5 spills, 10.3 h, 19 Oct to 20 Oct5 spills, 10 h, 11 Nov to 12 Nov11 spills, 69.5 h, 14 Nov to 17 Nov6 spills, 13.3 h, 18 Nov to 19 Nov31 spills, 31 h, 23 Nov to 24 Nov4 spills, 1 h, 28 Nov to 28 Nov31 spills, 59 h, 29 Nov to 2 Dec2 spills, 2 h, 4 Dec to 4 Dec27 spills, 74.8 h, 5 Dec to 10 Dec12 Dec 2025 11:15 GMT, 75 min15 spills, 24.3 h, 15 Dec to 16 Dec10 spills, 48.3 h, 17 Dec to 19 Dec8 spills, 26.8 h, 21 Dec to 23 DecHuddersfield STW14 spills, 31.3 h, 1 Jan to 2 Jan29 spills, 54.8 h, 5 Jan to 8 Jan35 spills, 13.3 h, 13 Jan to 15 Jan2 spills, 1 h, 24 Jan to 24 Jan15 spills, 6.8 h, 27 Jan to 28 Jan3 spills, 3.5 h, 23 Feb to 24 Feb3 spills, 8.5 h, 22 Mar to 23 Mar27 May 2025 01:00 GMT, 15 min4 spills, 2.3 h, 6 Jun to 6 Jun2 spills, 3.3 h, 6 Jul to 7 Jul2 spills, 1.8 h, 15 Jul to 15 Jul3 spills, 0.8 h, 19 Jul to 19 Jul6 spills, 3.5 h, 20 Jul to 20 Jul4 Sep 2025 14:45 GMT, 60 min5 spills, 3.5 h, 11 Sep to 11 Sep2 spills, 3 h, 15 Sep to 16 Sep4 spills, 5.8 h, 17 Sep to 17 Sep20 Sep 2025 12:30 GMT, 18.5 h3 spills, 4.8 h, 28 Sep to 28 Sep11 spills, 13.5 h, 4 Oct to 4 Oct8 spills, 12.8 h, 19 Oct to 20 Oct7 spills, 2.5 h, 27 Oct to 27 Oct2 spills, 1 h, 1 Nov to 1 Nov3 spills, 2.3 h, 11 Nov to 12 Nov3 spills, 2.8 h, 12 Nov to 12 Nov24 spills, 50.5 h, 14 Nov to 16 Nov10 spills, 6.3 h, 18 Nov to 19 Nov11 spills, 5.8 h, 23 Nov to 24 Nov28 Nov 2025 14:30 GMT, 75 min8 spills, 6.3 h, 29 Nov to 29 Nov22 spills, 9 h, 1 Dec to 1 Dec20 spills, 15 h, 5 Dec to 7 Dec33 spills, 32.5 h, 8 Dec to 10 Dec11 spills, 12.3 h, 15 Dec to 16 Dec14 spills, 17.8 h, 17 Dec to 19 Dec19 spills, 13.8 h, 21 Dec to 22 DecHuddersfield STW2 spills, 29.5 h, 1 Jan to 2 Jan5 spills, 55 h, 5 Jan to 8 Jan13 Jan 2025 13:45 GMT, 60 min4 spills, 3.3 h, 23 Jan to 24 Jan2 spills, 2.5 h, 26 Jan to 27 Jan20 Feb 2025 15:15 GMT, 45 min2 spills, 3.3 h, 23 Feb to 23 Feb26 Feb 2025 07:45 GMT, 90 min7 Mar 2025 06:15 GMT, 45 min22 Mar 2025 17:15 GMT, 4.5 h21 Apr 2025 19:00 GMT, 45 min26 May 2025 21:45 GMT, 45 min2 spills, 1 h, 5 Jun to 6 Jun10 Jun 2025 00:15 GMT, 15 min3 spills, 4.8 h, 6 Jul to 7 Jul2 spills, 3.3 h, 15 Jul to 15 Jul19 Jul 2025 15:00 GMT, 105 min20 Jul 2025 13:30 GMT, 90 min6 spills, 3.8 h, 3 Sep to 4 Sep7 Sep 2025 13:45 GMT, 45 min8 Sep 2025 16:45 GMT, 45 min2 spills, 3.3 h, 11 Sep to 11 Sep4 spills, 2 h, 15 Sep to 16 Sep2 spills, 4.5 h, 17 Sep to 17 Sep2 spills, 19.3 h, 20 Sep to 21 Sep28 Sep 2025 00:30 GMT, 3.3 h1 Oct 2025 06:45 GMT, 75 min12 spills, 18.8 h, 2 Oct to 4 Oct2 spills, 6.3 h, 19 Oct to 20 Oct20 Oct 2025 19:00 GMT, 15 min23 Oct 2025 00:00 GMT, 60 min26 Oct 2025 19:15 GMT, 30 min2 spills, 0.5 h, 31 Oct to 31 Oct1 Nov 2025 09:00 GMT, 105 min3 spills, 1.5 h, 4 Nov to 4 Nov7 spills, 4.8 h, 11 Nov to 12 Nov2 spills, 64.5 h, 14 Nov to 16 Nov3 spills, 3.3 h, 18 Nov to 19 Nov10 spills, 20.8 h, 23 Nov to 24 Nov5 spills, 8.3 h, 28 Nov to 29 Nov6 spills, 9 h, 1 Dec to 1 Dec14 spills, 10 h, 5 Dec to 7 Dec7 spills, 20.8 h, 8 Dec to 9 Dec3 spills, 1.8 h, 12 Dec to 12 Dec5 spills, 14 h, 15 Dec to 15 Dec2 spills, 15.8 h, 17 Dec to 19 Dec21 Dec 2025 21:15 GMT, 11.3 hHuddersfield STW4 spills, 31 h, 1 Jan to 2 Jan2 spills, 51 h, 5 Jan to 7 Jan23 Feb 2025 20:30 GMT, 2.5 h22 Mar 2025 17:45 GMT, 4.5 h6 Jun 2025 05:30 GMT, 105 min6 Jul 2025 20:00 GMT, 90 min15 Jul 2025 20:45 GMT, 15 min20 Jul 2025 14:15 GMT, 90 min4 Sep 2025 13:30 GMT, 90 min8 Sep 2025 17:00 GMT, 30 min2 spills, 1.3 h, 11 Sep to 11 Sep17 Sep 2025 05:45 GMT, 4.5 h20 Sep 2025 12:15 GMT, 17.5 h28 Sep 2025 00:45 GMT, 3.8 h3 spills, 12.3 h, 3 Oct to 4 Oct3 spills, 8.5 h, 19 Oct to 20 Oct1 Nov 2025 09:30 GMT, 15 min11 Nov 2025 21:45 GMT, 105 min2 spills, 37.8 h, 14 Nov to 16 Nov2 spills, 3 h, 18 Nov to 19 Nov23 Nov 2025 13:15 GMT, 2 h28 Nov 2025 13:30 GMT, 90 min3 spills, 2.8 h, 29 Nov to 29 Nov6 Dec 2025 18:00 GMT, 2 h7 Dec 2025 15:45 GMT, 60 min9 Dec 2025 04:15 GMT, 14 h15 Dec 2025 12:30 GMT, 6.3 h2 spills, 8.8 h, 17 Dec to 18 Dec21 Dec 2025 22:00 GMT, 6.5 h

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.

02M4M6M8MJan 2025: 586 h spilling ≈ 2.8 million m³ (range 1.1 million-7.0 million m³)JanFeb 2025: 17 h spilling ≈ 82,086 m³ (range 32,697-206,081 m³)FebMar 2025: 30 h spilling ≈ 143,295 m³ (range 57,077-359,748 m³)MarApr 2025: 0.8 h spilling ≈ 3,796 m³ (range 1,512-9,530 m³)AprMay 2025: 2.5 h spilling ≈ 11,862 m³ (range 4,725-29,780 m³)MayJun 2025: 13 h spilling ≈ 63,581 m³ (range 25,326-159,623 m³)JunJul 2025: 34 h spilling ≈ 163,223 m³ (range 65,015-409,779 m³)JulAug 2025: 0.0 h spilling ≈ 0.0 m³ (range 0.0-0.0 m³)AugSep 2025: 141 h spilling ≈ 669,026 m³ (range 266,487-1.7 million m³)SepOct 2025: 116 h spilling ≈ 548,507 m³ (range 218,482-1.4 million m³)OctNov 2025: 370 h spilling ≈ 1.8 million m³ (range 699,292-4.4 million m³)NovDec 2025: 442 h spilling ≈ 2.1 million m³ (range 835,371-5.3 million m³)Dec
Cubic metres (m³), estimate. Hours are measured by the event duration monitor.

Longest single spills

Started (GMT)OverflowDurationEstimated volume
14 Nov 2025, 05:45Huddersfield STW2.7 days121,431 - 765,357 m³
5 Jan 2025, 16:30Huddersfield STW2.2 days99,224 - 625,389 m³
5 Jan 2025, 17:15Huddersfield STW2.1 days95,916 - 604,543 m³
14 Nov 2025, 08:15Huddersfield STW1.8 days83,632 - 527,114 m³
5 Jan 2025, 17:00Huddersfield STW1.6 days72,764 - 458,619 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 estimate8.3 million m³range 3.3 million - 20.9 million m³
In litres8.3 billionrange 3.3 billion - 20.9 billion L
Olympic swimming pools3,329at 2,500 m³ each
Organic load, as people's raw sewage12.5 millionperson-days of untreated BOD

Assumed spill rate while spilling: 525.0 - 3,308.9 L/s (central 1,318.0 L/s), from a dry-weather flow of 525.0 L/s.

Pollutant releasedLowCentralHighConcentration used (low / typical / high)
BOD₅ (organic load) 132,586 kg748,939 kg4.2 million kg 40 / 90 / 200 mg/L
Low/high: Europe range, Ellis & Jenkins 2005; typical: UK, Ellis & Jenkins 2005 (both via botturi)
Suspended solids 348,038 kg3.5 million kg15.1 million kg 105 / 425 / 721 mg/L
Low/high: Europe range; typical: UK, Ellis & Jenkins 2005 (via botturi)
Ammonium-N 6,298 kg52,426 kg194,292 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 3,978 kg21,636 kg112,814 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 331.5 trillion organisms8.3 × 10¹⁵ organisms2.1 × 10¹⁷ 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.

Huddersfield STW

Storm tank at sewage works · discharges to River Calder & River Colne

Spills 2025
82 (781 hours) · down 38% on 2024
Spills 2024
132 (1,621 hours)
Long-term average
105.0 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
Env Act (SODRP) investigation completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
River Colne from River Holme to River Calder (GB104027062550)
Outlet location
SE1725019480 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS01394 · WRA7409 · company name: DEIGHTON/STW

Huddersfield STW

Storm tank at sewage works · discharges to River Calder & River Colne

Spills 2025
60 (372 hours) · down 32% on 2024
Spills 2024
88 (864 hours)
Long-term average
83.7 spills a year (monitored since 2020)
Monitor uptime
98% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
Env Act (SODRP) investigation completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Calder from Ryburn Confluence to River Colne (GB104027062642)
Outlet location
SE1729021120 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS01395 · WRA7409 · company name: BRIGHOUSE/UPPER STW/3XDWF OVERFLOW

Huddersfield STW

Inlet overflow at sewage works · discharges to River Calder & River Colne

Spills 2025
72 (369 hours) · down 16% on 2024
Spills 2024
86 (451 hours)
Long-term average
71.8 spills a year (monitored since 2020)
Monitor uptime
100% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
Env Act (SODRP) investigation completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
River Colne from River Holme to River Calder (GB104027062550)
Outlet location
SE1697019070 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS01396 · WRA7409 · company name: DEIGHTON/STW

Huddersfield STW

Inlet overflow at sewage works · discharges to River Calder & River Colne

Spills 2025
40 (231 hours) · down 18% on 2024
Spills 2024
49 (304 hours)
Long-term average
53.0 spills a year (monitored since 2020)
Monitor uptime
94% of the year
High-spill reason (company)
Not asset maintenance - hydraulic capacity
Investigation
Env Act (SODRP) investigation completed, UWWTR investigation completed, Operational investigation completed
Improvement
No improvement action in reporting period
WFD catchment
Calder from Ryburn Confluence to River Colne (GB104027062642)
Outlet location
SE1729021120 (OS grid reference) · View on Apple Maps
EA ID / permit
YWS01397 · WRA7409 · company name: BRIGHOUSE/UPPER STW/6XDWF OVERFLOW

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 Yorkshire 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.