The regulator Ofwat has expanded its investigation into the dumping of raw sewage to include South West Water after finding “shocking” failures in the way the majority of water companies run their waste treatment works.

Ofwat said on Tuesday it had extended its inquiry after heightened concerns about South West Water’s environmental performance and suggestions it was not complying with its legal obligations.

The enforcement action being taken by the regulator is part of a large inquiry into potentially illegal dumping of raw sewage by privatised water companies. Six out of nine companies – Anglian Water, Northumbrian Water, Thames Water, Wessex Water, Yorkshire Water and now South West Water – have been served formal notices to gather further information for enforcement purposes, the regulator said.

The Ofwat statement says: We continue to progress the five enforcement cases we opened in March 2022. In addition, we have opened a new enforcement case, into South West Water. This is due to our heightened concerns about its environmental performance across a number of metrics, that may suggest it is not complying with obligations Ofwat has powers to enforce. We have now issued South West Water with an information request under our formal enforcement powers to explore this further.

Beyond our enforcement cases, all water and wastewater companies in England and Wales remain subject to our on-going investigation into whether their wastewater treatment works are operating as they should. In July we will be writing to the remaining five companies to request updates on the progress of the plans they submitted to us in December setting out how they would address the issues they had identified at their treatment works and more generally improve their management of their environmental obligations.

The full statement from Ofwat can be read here and the Guardian report here.