Ofwat announced it has opened enforcement cases into four more firms as part of its investigation into utilities' management of wastewater treatment works.

The investigations have been opened following a "detailed analysis" of companies' environmental performance and how often they spill wastewater from storm overflows.

It was this analysis that "heightened Ofwat's concerns" that the four utilities may not be fulfilling environmental protection and pollution-minimising obligations.

The firms newly subject to this inspection are Dwr Cymru Welsh Water, Hafren Dyfrdwy, Severn Trent and United Utilities, Ofwat announced on Tuesday morning.

They join other companies that have been under investigation since 2022: Anglian Water, Northumbrian Water, South West Water, Thames Water, Wessex Water, and Yorkshire Water. Southern Water is still being monitored by Ofwat following an enforcement case in 2019.

Amid increased scrutiny on water companies regarding pollution, sewage discharges, and their financial viability, there's a growing emphasis on their operational transparency and future billing plans.

Analysis of official Department for Environment, Food & Rural Affairs data revealed that sewage was discharged into designated bathing waters an average of 86 times daily in 2023. Meanwhile, Environment Agency statistics indicated that untreated sewage discharges soared from 1.8 million hours in 2022 to a record 3.6 million hours in 2023.

In response, UK Information Commissioner John Edwards urged utility firms in England, Wales, and Northern Ireland to proactively disclose monthly data on sewage outflows. This initiative aims to enhance public trust by providing timely information without the need for individual requests.

The largest and most complex investigation

This development means that all wastewater companies in England and Wales are now under enforcement action, highlighting Ofwat's significant concerns about the sector's environmental performance, according to Ofwat chief executive David Black.

"This is the largest and most complex investigation Ofwat has undertaken. However, Ofwat is committed to concluding these cases as quickly as possible," he emphasized.

While there are 14 water providers in England and Wales, only 11 of them also function as wastewater companies.

What next?

Ofwat clarified that opening an enforcement case does not automatically indicate a breach of legal obligations. Severn Trent has already outlined plans to significantly reduce the use of storm overflows, which Ofwat has positively acknowledged.

During its investigation, Ofwat will assess the historical and current wastewater performance of the companies to determine whether any regulatory action is warranted.

In cases where regulatory breaches are identified, fines can be imposed. In recent years, penalties exceeding £300 million have been imposed on water and wastewater companies.

United Utilities stated, "We recognize and share public concerns regarding environmental health and wastewater system operations, including combined sewer overflows."

Severn Trent indicated its commitment to surpassing industry standards in addressing sewage overflows, stating it aims to lead in this area.

Both companies expressed their intention to collaborate closely with Ofwat throughout its investigation.