Southern Water has seen its Environment Agency environmental performance rating fall from 2 stars in 2024 to just 1 star in 2025, the lowest possible rating under the regulator’s 4-star assessment system.
The damning figures have been revealed in a new joint report published yesterday (Thursday), by the Drinking Water Inspectorate, Environment Agency, Natural Resources Wales and Ofwat, alongside a detailed assessment of Southern Water’s environmental performance.
The company has seen its Environment Agency rating fall from 2 stars in 2024 to just 1 star in 2025, the lowest possible rating under the 4-star assessment system.
It is the 4th time Southern Water has received the lowest rating since environmental performance assessments began in 2011, having previously been classified as poor performing in 2013, 2019 and 2021.
The latest assessment reveals that Southern Water failed to meet its targets in 4 of the 6 environmental performance measures, with regulators raising serious concerns about pollution, wastewater treatment and delays in delivering environmental improvements.
Of the 301 pollution incidents recorded across Southern Water’s operating area, 253 originated from sewerage infrastructure, while a further 48 were linked to water supply assets.
The 12 serious pollution incidents were all associated with sewerage infrastructure, with 8 involving rising mains, 2 involving foul sewers, 1 at a pumping station and 1 at a sewage treatment works.
Although the number of serious incidents fell from 15 in 2024 to 12 in 2025, the company’s performance remained significantly below the Environment Agency’s required standard.
Southern Water also recorded 64 sewerage pollution incidents per 10,000km of sewer network, considerably above the sector figure of 41.
The figures cover Southern Water’s wider operating area, which includes the Isle of Wight, rather than incidents occurring exclusively on the Island.
The company was also found to be failing environmental discharge standards at 11 sewage treatment works, more than double the 5 sites recorded in 2024.
Its compliance with permitted limits for pollutants in treated wastewater fell from 98.2% in 2024 to 96.7% in 2025, resulting in another red rating from the Environment Agency.
Further concerns were raised over Southern Water’s failure to complete environmental improvement schemes within agreed deadlines.
Of the 37 environmental improvement actions assessed in the joint report, only 27 were delivered on time, representing a completion rate of 73%.
A narrower measure used in the Environment Agency’s star-rating assessment showed an even poorer result, with just 10 of 20 qualifying schemes completed within their deadlines.
There were, however, some improvements in Southern Water’s performance.
The company self-reported 84% of its pollution incidents, up from 82% in 2024, helping regulators identify problems and respond more quickly.
Its drinking water quality also remained high, with 99.98% of tests meeting the required standards.
Water supply interruptions improved considerably, with the average number of minutes lost per property falling by 96% compared with the previous year – described by regulators as Southern Water’s strongest-ever performance in this area.
Leakage was also reduced by 8.1%, with an estimated 76.6 litres lost per property each day, below the industry average of 104.5 litres.
Despite these improvements, the company recorded a 40% increase in internal sewer flooding incidents compared with the previous year, while customer satisfaction was the lowest of all 17 water companies assessed.
Southern Water has also been placed under a Drinking Water Inspectorate transformation programme, intended to tackle weaknesses in risk management and safeguard future water supplies.
The company, which serves more than 4.7 million people across its operating area, has around £8.9billion of investment to deliver between 2025 and 2030.
Regulators say that investment must translate into improvements in environmental performance, reliability and customer service.
Philip Duffy, Chief Executive at the Environment Agency, has said:
“People expect two simple things: safe water from their taps and clean, healthy rivers. Today’s report shows good performance on drinking water quality, but on wastewater and pollution the sector is still falling short.
“We are stepping up inspections and enforcement and will use our powers to hold water companies to account and drive the improvements people and the environment deserve.”
Helen Campbell, Interim Executive Director for Delivery at Ofwat, has said:
“Customers rightly expect the record investment approved by Ofwat to deliver tangible improvements in their daily lives and for the environment.
“Over the past year we have seen some step up to this challenge, but this is inconsistent and poor performance continues in too many places.
“The responsibility sits with water companies to deliver on what they have agreed to, and we will continue to work across regulators to drive stronger outcomes.”
The latest findings come as the 4 regulators publish their first combined Water Industry Performance Insights report, bringing together information on drinking water quality, environmental performance and customer service.
Southern Water’s poor environmental rating places further pressure on the company to demonstrate that improvements are being made, particularly in preventing pollution, maintaining sewage infrastructure and protecting waterways.
For Isle of Wight residents, the findings provide a wider picture of the performance of the company responsible for the Island’s water and wastewater services, although the published company-wide figures do not identify how many of the recorded incidents occurred locally.
