Deep Dive

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.

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The table shows the average spills per asset per water company between 2021 and 2023 and the percentage difference.

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

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

🔗 Scottish Water Data