Water regulator Ofwat has opened four new enforcement cases against water and wastewater companies, with formal notices served on FTSE 100 firms Severn Trent PLC (LSE:SVT) and United Utilities Group PLC (LSE:UU.).
Dŵr Cymru Welsh Water, and Hafren Dyfrdwy have also been told to gather evidence.
It follows a detailed analysis by Ofwat of their environmental performance and the rate at which these companies spill from storm overflows.
Following this latest round of enforcement cases, all 11 water and wastewater companies across England and Wales are or have been, under investigation by Ofwat for how they treat sewage and wastewater.
It “demonstrates how concerned we are about the sector’s environmental performance”, said Ofwat’s chief executive David Black.
“Where we find that companies have breached their obligations, we will continue to act – over recent years, we have imposed penalties and payments of over £300 million on water and wastewater companies.”
Ofwat first opened an investigation into Southern Water in 2019, before bringing cases against Anglian Water, Northumbrian Water, South West Water, Thames Water, Wessex Water, and Yorkshire Water in 2022.
Sewage contamination in British rivers and coastlines has become a source of national outrage in recent years.
Earlier this month, the Supreme Court ruled that the Manchester Ship Canal Company can bring a claim against United Utilities in relation to discharges of foul water contaminated with untreated sewage.
Analysts believe this could lead to a groundswell of similar claims against other water companies across Britain.
Despite a litany of pollution scandals, water companies recently sought permission from Ofwat to raise customer bills as much as 91% over the next five years.
Ofwat largely denied these requests, allowing an average hike of 21% instead.