South West Water has been given the lowest possible environmental rating by the Environment Agency over high levels of pollution.

The regulator downgraded the firm from two stars out of a possible four to one, meaning it is now considered a “poor performing company” for its environmental impact.

It said it had performed “significantly below target” for sewage pollution incidents for the 15th year in a row.

South West Water, which has 1.8 million customers across Devon, Cornwall, the Isles of Scilly and parts of Dorset and Somerset, said it knew there was “much more to do” and was taking action to improve areas that “matter most” to customers and the environment.

The annual Environmental Performance Assessment grades England’s nine water and sewerage companies largely on how often they pollute rivers, streams and the sea.

For 2025, South West Water was among four companies rated as poor performing, or one star, while four others were rated as requiring improvement, two stars.

Severn Trent Water was the only company to achieve the highest rating of four stars.

Industry regulator Ofwat said South West Water met seven of its 23 targets in 2025-26, with below target performance for “most areas”.

It noted its performance in relation to water supply interruptions “deteriorated substantially” and, despite improving annual performance by 38%, said the company’s total pollution incidents performance remained more than double its target.

Customer satisfaction also remained challenging, ranking 15 out of 17 in the sector.

While storm overflows performance improved by 19%, it still fell short of its target, the Environment Agency said.

It was, however, the only company to have met its target for internal sewer flooding, or how often wastewater enters a property, every year since 2020-21.

A spokesperson for South West Water said: “We are under new management with a renewed focus on improving our performance.

“We know there’s much more to do and although it will take time, we are taking action and making progress in the areas that matter most to our customers and the environment.”

They said the firm had “reduced spills from storm overflows by 17% last year alone, with spill duration down by 25%, and we have insourced over 40 new leakage specialists”.

“We are working hard to build on the progress we’re making, backed by record levels of investment across the region,” the spokesperson said.

“We are transforming our network to improve long-term resilience of our water supply; protecting the environment and tackling leaks as part of our multibillion-pound plan to deliver the long-term improvements our customers and communities expect.”

A separate report from the Drinking Water Inspectorate, the Environment Agency, Natural Resources Wales and Ofwat said South West Water’s drinking water quality “remains exceptional, and consumers can be confident that their water is safe to drink”.

It noted although its internal sewer flooding performance had deteriorated, “it is still performing better than the industry average”.

However, it said overall environmental performance “is poor”.

In a summary, the report said overall water supply interruptions “remain a significant concern, and it is one of the worst performers in the industry”.

To improve the company needed to reduce interruptions and complete a transformation programme to address the root causes of its failures and “substantially improve customer interactions and overall experience”, it said.

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