In 2023, there were a total of 464,056 sewage discharges into English rivers, waterways, and seas, averaging 1,271 sewage spills per day. This amounted to a staggering 3.6 million hours (about 410 and a half years) of sewage spills into English waterways over the course of the year.

Spills this decade

When we include EDM data from Wales, Scotland and Northern Ireland, there was a total of 584,001 spills in 2023. This is a 42% increase from 411,927 sewage spills in 2020. Forecasting shows that if these trends were to continue with impunity, then by 2035 there would be over 1 million sewage spills per year.

This report will demonstrate that the UK sewage scandal is likely far more extensive than currently estimated, with varying impacts across different areas and will only get worse if governments continue not to act. By conducting a deep dive into the data on sewers, bathing waters, and rivers, as well as examining differences in other devolved nations of the UK and constituencies, this report will reveal the sheer number and hours of sewage that was spilled last year.

2020202120222023Total
Anglian Water17,42821,35116,08231,62386,484
Northumbrian Water32,49736,48329,69746,492145,169
Scottish Water12,72510,71514,05215,28952,781
Severn Trent Water60,98259,68444,76560,253225,684
South West Water42,05342,48437,64958,249180,435
Southern Water19,78219,07716,68829,49485,041
Thames Water18,44314,7138,01416,99058,160
United Utilities113,94081,58869,24597,537362,310
Welsh Water88,52874,006108,860271,394
Wessex Water28,99423,52421,87841,453115,849
Yorkshire Water65,08370,06254,27377,761267,179

EDMs Explained

Before diving deep into the sewage data, let’s take a minute to reflect on what EDM systems are and why the data is useful.
Event Duration Monitoring (EDM) is a method used to measure and record the duration and frequency of sewage overflows, and are installed on permitted assets discharging to Water Framework Directive water bodies, which are:

  1. Combined sewer overflows (CSOs) on the sewer network including pumping stations
  2. Storm overflows at the inlet to sewage treatment works (STWs)
  3. Storm discharges from storm tanks at STWs

The EDM system uses sensors and data loggers installed at overflow points. These devices detect and record the start and end times of overflow events, capturing the duration and frequency of discharges. Each water company has a discharge permit, which allows a certain amount of sewage to be discharged, monitoring and reporting requirements form part of this permit.

The data collected through EDM helps regulatory bodies, environment agencies, and water companies understand the patterns and impact of sewage overflows. This information is crucial for improving wastewater management practices, upgrading infrastructure, and ensuring compliance with environmental regulations. In the context of the UK sewage scandal, EDM data has become critical in illustrating the scale and frequency of sewage discharges.

However, this data is not without its challenges and limitations. Currently, this data is focused on the hours and number of spills, not the volume of sewage entering our waterways. This means that the actual amount of sewage entering bodies of water is unknown and therefore makes this data somewhat unreliable.

The limitations of EDM as a method for calculating the amount of sewage going into our waterways will be examined later in this report.

Average spills per asset between 2021 and 2023

South West Water and United Utilities have consecutively poor performance when looking at average spills per assets between 2021 and 2023. Since 2021, South West Water has seen a 14% increase in the average spills per asset. 2022 overall seemed a slightly better year for water companies’ average number of spills per asset, with a decrease in average spills per asset across the board. However, 2023 saw all water companies’ average spill per asset increase, with Wessex Water seeing a 69% increase between their average spills per asset in 2022 and 2023. However, while Wessex Water saw the biggest increase by way of percentage difference, the worst performing was South West Water with an average spill per asset of 52.1.

Based on this data, the water companies are ranked (Best to worst) as follows:

  1. Anglian Water
  2. Northumbrian Water
  3. Thames Water
  4. Southern Water
  5. Wessex Water
  6. Dwr Cymru
  7. Yorkshire Water
  8. United Utilities
  9. South West Water

There was a 63% difference between the worst and best performing water companies in 2023, with South West Water crowned as the worst and Anglian Water as the best for average spills per asset.

Spill forecasting based on average spills per asset

Based on the data above, future spill forecasting of what average spills per asset might look like in 2030 and 2035 was completed. This data shows that if present levels of spills continue, there will be an exponential increase for some water companies, while others will improve. This will then create a wider disparity and difference in the spills by the water companies.

Within this, Southern Water, South West Water and Wessex Water will continue to be the worst performing water companies, with Anglian Water being the cleanest by some fair stretch.

Water Company20302035
Anglian Water16.511.6
Dwr Cymru49.6560
Northumbrian Water47.4959.22
Severn Trent23.2720.69
South West Water69.8785.37
Southern Water72.86101.11
Thames Water27.2525.43
United Utilities59.6868.18
Wessex Water74.53103.51
Yorkshire Water48.2555.2

Sewers

From the data, it can be seen that 60% of sewage discharges come from the sewer network itself, with 20% from discharge at the sewer pump, 14% from storm tanks at wastewater and treatment works sites.

Turning to look at sewage treatment work sites more specifically, the table below shows the 5 worst sewage treatment works for number of spills. This table also shows the duration of spills and the operational site percentage. This data shows that Severn Trent Water had 4 of the top 5 worst performing sewage treatment works, with a total number of spills in the top 5 from their sites of 755. Furthermore, the Church Stretton Sewage works is listed as one of the worst performing, yet it only had an operational percentage of 68.5%, meaning that there was 31.5% of the year when this site was not operational.

Sewage Treatment WorksWater CompanyNo. of spillsDuration of spillsOperational %
Shrewton Water Recycling CentreWessex Water2626183.9299.78
Kimcote Sewage Treatment WorksSevern Trent Water2052364.34100
Northend Sewage Treatment WorksSevern Trent Water196243.8185.6
Church Stretton Sewage Treatment WorksSevern Trent Water1773852.168.5
Gaulby Sewage Treatment WorksSevern Trent Water1772669.399.7

Bathing waters

The table below shows the top 20 most polluted bathing waters in 2023. United Utilities had the most spills into their bathing waters, with 13 of the top 20 being within their catchment area. Meanwhile, South West Water has 3 in the top 20 polluted bathing waters, with Yorkshire Water, Thames Water, Northumbrian Water, and Southern Water making up the remainder of the top 20.

RankBathing WaterWater CompanySpills
1New BrightonUnited Utilities1,485
2St AnnesUnited Utilities1,290
3Plymouth Hoe (East)South West Water1,264
4AllonbyUnited Utilities871
5FleetwoodUnited Utilities781
6Wharfe at Cromwheel, IlkleyYorkshire Water742
7Wolvercote Mill StreamThames Water729
8SpittalNorthumbrian Water680
9Cowes, GurnardSouthern Water649
10WallaseyUnited Utilities613
11Walney Biggar Bank; Walney West Shore; Walney Sandy GapUnited Utilities514
12SeascaleUnited Utilities466
13Mothecombe BeachSouth West Water465
14East Looe BeachSouth West Water451
15Walney West ShoreUnited Utilities446
16Haverigg; Walney Biggar Bank; Walney West Shore; Walney Sandy GapUnited Utilities382
17Morecambe SouthUnited Utilities378
18West KirbyUnited Utilities354
19Southport; St Annes Pier; St. Annes North; Blackpool SouthUnited Utilities339
20FormbyUnited Utilities326

New Brighton: England’s most polluted bathing water?

New Brighton is a beach located on the North West coast of England, on the Wirral, Merseyside. Last year, New Brighton had 1485 spills, coming in top spot for the greatest number of spills in 2023. Not only did New Brighton come top for the number of spills in 2023, but it also came second for the duration of spills, with 12,769 hours of spills, constituting a year and a half in hours!

Rivers

Rivers are difficult to accurately calculate due to how the EDM data is presented. However, the below data shows the top 20 rivers by way of the number of sewage spills, with the percentage increase from 2022 figures.

In total, the top 20 rivers saw 55,209 instances of sewage spills across 458,725 hours in 2023! Overall, for rivers across England and Wales, it has been calculated that there have been 559,546 sewage spills in 2023. This figure means that our rivers have been hit worse than our beaches in terms of sewage pollution in 2023.
While the River Aire saw the highest number of sewage spills in 2023, the River Avon saw a dramatic increase of 77% on 2022 numbers. Each of these rivers has seen an increase in the number of spills from 2022 – a worrying trend.

RankRiverSewage Spills% increaseCompany
1River Aire488837Yorkshire Water
2River Avon471977Wessex Water
3River Calder417741Yorkshire Water
4River Irwell345745United Utilities
5Unknown335169South West Water
6River Tame318054United Utilities
7River Severn305738Severn Trent Water
8River Trent293957Severn Trent Water
9River Ouse277468Yorkshire Water
10River Derwent273238Severn Trent Water
11River Tawe259243Dwr Cymru Welsh Water
12River Teifi257937Dwr Cymru Welsh Water
13River Wharfe245646Yorkshire Water
14River Don223150Yorkshire Water
15River Eden202119United Utilities
16River Tamar199931South West Water
17River Usk186419Dwr Cymru Welsh Water
18Solent155053Southern Water
19River Torridge140649South West Water
20River Rother123758Southern Water

English operational performance and sites below 90% operational

Each water company can also be analysed for their EDM operational performance, and the average performance of their monitoring systems. It is expected that EDM will be over 90% in terms of the amount of time they are operational for. The table below shows that operational average performance for each water company.

Out of all 9 water companies, Wessex Water has the best in terms of average EDM operational performance, meanwhile Dwr Cymru is the worst. The average overall however is 93%, this is only just within the expected 90%. Therefore, each water company could do better at ensuring that their monitoring systems are working at full capacity. Without these sites working at full capacity, the data will always struggle to show the full picture of sewage spills; in fact, if sites are not fully operational it likely means that the reality is worse than the data.

Number of assets under 90% operational 
Wessex Water98.41
Anglian Water96.86
South West Water94.38
Northumbrian Water93.5
Severn Trent Water93.81
Southern Water92
United Utilities92.54
Yorkshire Water92.8
Thames Water90.3

Non-operational sites and sites below 90% operational

The data also includes sites that are no longer operational. During the analysis of other sections, these sites were excluded to avoid skewing the averages. There is potential that Water companies include non-operational sites in their data to improve their figures slightly. However, while these sites were excluded from other analyses, this section will specifically examine the non-operational sites.

302 sites in the data showed as no longer in operation. Anglian Water had the most sites showing as no longer operational, with 131 sites. Followed by Thames Water with 91 sites, Severn Trent with 46 sites, South West Water with 19 sites, United Utilities with 9 sites, Yorkshire Water with 5 and lastly Southern Water with 1. Wessex Water, Dwr Cymru and Northumbrian Water did not have any sites listed as no longer operational.

Other than sites that are no longer operational, there are also a number of sites that have performed less than 90% operationally. The table below shows the number of assets per water company that are performing under 90% operationally.

Number of assets under 90% operational 
Anglian Water97
Northumbrian Water206
Severn Trent Water414
South West Water175
Southern Water144
Thames Water152
United Utilities262
Welsh Water21
Wessex Water58
Yorkshire Water401
Total1930

Severn Trent Water and Yorkshire Water have the greatest number of assets that are under 90% operational.

When sites perform at less than 90% operational, then the water companies must give a reason as to why. The table below shows these reasons, as well as which reasons are stated most by water companies.

Reason for under 90%Number of times reason used
Access - unable to retrieve34
capital/maintenance works27
Comms failure/issue543
Installation set-up/design287
power failure/issue175
sensor failure/issue664
telemetry or data archival179

Worst-performing sites

The top 5 worst performing sites are below, these are sites that are above 0% operationally.

Sites with VERY little Data:
Other than sites no longer operational included in the data, sites that have minimal operational % also impact the reliability of the data. With monitors working at such a low level, it means that spills are likely not caught and therefore will not be contained in the data.

Name of siteWater CompanyOperational %
Lone Valley, WaterloovilleSouthern Water9.1
Fishmarket Road, RyeSouthern Water11
School Lane, DanehillSouthern Water12.7
Field End Garden, AshfordSouthern Water4
Earle Drive, Parkgate RoadDwr Cymru15.6

Looking deeper at Scottish Water

Scottish Water are currently only required to report on about 6% of their combined sewer overflows to the Scottish Environment Protection Agency (SEPA) in their annual EDM report.

They are since released additional data on the overflows that are not reported to SEPA, which means the true extent of sewage pollution in Scotland is becoming alarmingly more clear.

The total number of spills reported in the annual returns was 15,289. However, with the addition of new data, we now see that the true figure is 42% higher, making it actually 21,660.

Spills Reported to SEPASpills NOT Reported to SEPATotal
202012,725N/A12,725
202110,715N/A10,715
202214,0525,66819,720
202315,2896,37120,957

One surprising aspect of this data is the extremely high average number of spills per overflow in Scotland, which is 131. This is much higher than the average in England (33 spills per overflow) and Northern Ireland (21 spills per overflow). This suggests that Scotland may be experiencing more frequent or larger-scale wastewater spills compared to the other regions.

Northern Ireland release the truth

We have been in the dark for a long time regarding sewage discharges in Northern Ireland – but the period of guessing is coming to an end.

For the very first time, we have some EDM data from Northern Ireland.

In summary, 82 EDMs were actively monitoring, recording a total of 1,785 spills throughout 2023. On average, each overflow experienced 22 spills.

Total number of CSOs 2,333
Number of EDMs reporting82
Total Spills1,785
Forecasted Spills across all CSOs51,326
Average number of spills per overflow in Northern Ireland21
Storm overflows spilling fewer than 10 times in Northern Ireland36

Their worst preforming assets were:

Asset NameBathing Beach2023 spill count
Tullybrannigan Road CSONewcastle146
Curran Road Loughview CSOBrowns Bay126
The Diamond Ballycastle CSOBallycastle120
Articlave CSOPortstewart115
Sandy Bay WwPSBrowns Bay86
Bushfoot WwPSPortballintrae Salmon Rock82
Bonamargy WwPSBallycastle70
Red Bay WwPSWaterfoot69
Orlock Sandeel WwPSGroomsport68
Ballyhaskin WwPSMillisle55

NI Water claims in their annual report that they are installing Event Duration Monitors (EDMs) across its wastewater network to track and record CSO discharges. Allegedly, by the end of the PC21 Price Control period (ending in spring 2027), NI Water plans to have over 700 EDMs in place, covering around 30% of all storm overflows. They state that this is part of a £20 million program aimed at improving monitoring and compliance. However, it’s worth questioning whether this investment will truly lead to significant improvements or if it’s merely a superficial solution to deeper infrastructure issues.

Limitations and discrepancies in Event Duration Monitoring

There are key issues with EDM operation reporting percentages which impact this data. Water companies must ensure that monitors are working to collect as accurate a picture as possible for the data’s reliability. However, unreliable data from EDM sensors means that water companies and regulatory bodies such as the Environment Agency cannot effectively monitor and regulate sewage discharges. Therefore, while having this data is helpful to gauge how water companies are performing when it comes to polluting our waters, it is likely that the picture is much worse than this data suggests, which is a bleak thought. Moreover, 2023 saw the completion of installation of spill monitors at every storm overflow in England. Therefore, when analysing the data it needs to be kept in mind that not all storm overflows had monitors installed and working in 2020 – 2022. This means care needs to be taken with comparisons over time. However, despite these issues, the data still shows an increase in sewage spills that cannot be explained by the installation of more monitors alone.

It also seems that there is a discrepancy between the legislative language, statements made by government ministers, and the actual monitoring practices by the Environment Agency. This discrepancy lies in how sewage spills are monitored, with an issue between volume and time. Currently, EDM measures sewage spills in hours and not volume. However, the Environment Act 2021 section 80 subsection 2(b) mandates that the Secretary of State must develop a plan aimed at reducing the volume of discharges from storm overflows in England. Similarly, former Water Minister Rebecca Pow stated that “the volume of sewage being discharged into our waters is unacceptable and we are taking action to make sure polluters are held to account”. However, the Environment Agency requires outfalls to have Event Duration Monitoring sensors, but these sensors track duration of discharge and not their volume. This indicates a misalignment between what is being monitored and what the law and government ministers are focusing on.

Summary

The data shows that sewage spills from water companies are on the rise. Future forecasts indicate that if current trends continue, the situation will only worsen. Each water company was underperforming in at least one of the areas examined, except Anglian Water, who were the best performing water company overall. South West Water was ranked the worst water company in 2023 for the number of spills per asset. Wessex Water and Severn Trent Water had the worst performing sewage treatment works. United Utilities were the worst for polluting bathing waters.

Water companies need to be held to account for the damage they are causing to our waterways, the time has come for them to stop polluting with impunity.

We’re calling for action!

From the analysis of the EDM data, Surfers Against Sewage are calling on the next government to:

Reveal the truth:

We need UK-wide transparency about sewage pollution.

Accurate and accessible real-time water quality information year-round
A transparent bathing water application process
Water quality testing that shows the full picture
Transparency across the sewage system

Prioritise high risk pollution:

Take immediate targeted action to tackle the highest risk pollution events.

End untreated discharges affecting bathing waters and popular water usage areas by 2030
End untreated discharges affecting high priority nature sites by 2030

About this data investigation:

2023 Water Quality Deep Dive

Written by: Eleanor Godwin & Annie McKelvey

Published: 10 September 2023

Reading time: 20 mins

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