The regulator Ofwat has opened an enforcement case against South West Water as part of its ongoing investigation into how companies manage wastewater treatment.

Ofwat has opened enforcement cases into ongoing concerns and the latest performance data on South West Water’s environmental performance. The company has now been served with a formal notice to gather further information for enforcement purposes.

A South West Water spokesperson said: “South West Water notes the announcement by Ofwat today and we are taking Ofwat’s decision very seriously.

"This will reduce our use of storm overflows, maintain our region’s excellent bathing water quality standards all year round and reduce and then remove our impact on river water quality by 2030.

"We will continue to work openly and transparently with Ofwat as part of their industry wide activity.”

South West Water joins Anglian Water, Northumbrian Water, Thames Water, Wessex Water and Yorkshire Water, all having enforcement cases raised against them.

As well as South West Water, the five enforcement cases opened in March are continuing as Ofwat still has concerns, some serious, arising from the information provided to Ofwat, both in December last year and in response to formal notices issued by the regulator.

This is to ask and understand more about those concerns and, where things have gone wrong, to seek further assurances that things are being put right as quickly as possible.

Particular areas of concern include issues about the quality and completeness of the information companies have about how their wastewater treatment works are performing; and, what they do with that information to ensure the works are adequate, operating correctly and not causing environmental harm, such as through sewage discharges.

All wastewater companies in England and Wales remain subject to the ongoing investigation.

Ofwat will keep the focus of its enforcement cases under review, and the companies in focus may change as new information comes to light.

Ofwat will shortly be writing to the remaining companies to request updates on the progress of remediation plans they submitted to Ofwat in December.

A spokesperson for South West Water said: "We will provide any further information required as part of its review into South West Water. It is important that Ofwat and the public can have ongoing confidence in our commitment to the environment. Earlier this year we conducted a line by line review of our plans and announced our largest environmental programme in 15 years.

"This will reduce our use of storm overflows, maintain our region’s excellent bathing water quality standards all year round and reduce and then remove our impact on river water quality by 2030. We will continue to work openly and transparently with Ofwat as part of their industry wide activity.”

David Black, Ofwat chief executive, said: “The serious concerns we identified last year prompted our initial focus on five companies.

"As we gather and analyse more information, including data on storm overflow spills, our concerns have grown further about South West Water’s operation of its wastewater assets and environmental performance.

"As a result, we have opened an additional enforcement case into South West Water.

“We have now opened enforcement cases against the majority of wastewater companies in England and Wales.

"From what we have seen so far, the scale of the issue here is shocking – companies must resolve any problems at wastewater treatment works and do so quickly. Where they have breached their obligations, we will not hesitate to act.”

As the investigation continues, Ofwat expects all companies to make quick progress to address non-compliance and strengthen the management of their environmental obligations as a whole.

Ofwat is working closely with the Environment Agency, who are carrying out a criminal investigation into companies’ compliance with environmental permits.