Water regulator Ofwat set to investigate all 11 water companies in England and Wales over potential illegal sewage spills

All 11 water firms in England and Wales are under scrutiny by Ofwat as part of a major investigation into sewage pollution in rivers.

The water regulator said it showed 'how concerned we are about the sector's environmental performance'.

Ofwat announced it had served formal enforcement notices on four remaining utilities firms - Dwr Cymru Welsh Water, Hafren Dyfrdwy, Severn Trent and United Utilities - who up to now had not been investigated.

It means the firms may have breached their obligations to protect the environment, which could lead to fines.

Ofwat opened a major investigation in November 2021 into the companies' sewage treatment works.

It has handed fines amounting to more than £300million in recent years to the companies it found to have breached their legal duties.

The regulator has already taken out enforcement cases against Anglian Water, Northumbrian Water, South West Water, Thames Water, Wessex Water and Yorkshire Water, with extensive investigations ongoing.

It is also still monitoring Southern Water following a previous enforcement case in 2019.

Every major English water company has reported data suggesting they have discharged raw sewage when the weather is dry - a potentially illegal practice.

Water companies can release untreated sewage into rivers and seas when it rains to prevent it flooding homes, but such spills are unlawful when dry.

David Black, Ofwat's chief executive, said: 'The fact that Ofwat now has enforcement cases with all 11 of the wastewater companies in England and Wales demonstrates how concerned we are about the sector's environmental performance.

'This is the largest and most complex investigation Ofwat has undertaken.' 

But Mr Black said the regulator wants to conclude the cases 'as quickly as possible', so that the sector can focus on spending £88billion as part of its latest plan to 'deliver cleaner rivers and seas'.

United Utilities said in a statement: 'We understand and share people's concerns about the health of the environment and the operation of wastewater systems, including combined sewer overflows.' 

Severn Trent said it had 'committed to going further and faster than anyone else in the sector' in relation to tackling sewage overflows.

Both firms said they would 'work constructively' with Ofwat in its investigation.

A spokesman for the Government's Environment Department said: 'We will never look the other way while water companies pump sewage into our waterways. 

'That is why we welcome the enforcement action announced today.

'The new Government will go even further to clean up Britain's rivers, lakes and seas.'

Last week, Prime Minister Sir Keir Starmer said the Government will need to 'get to grips with' sewage and pollution, while Environment Secretary Steve Reed proposed new measures to reform the sector and 'fix our broken sewage system'.

It followed Ofwat setting out new plans aimed at delivering a 44 per cent reduction in spills from storm overflows compared to levels in 2021.

United Utilities said in a statement: 'We understand and share people's concerns about the health of the environment and the operation of wastewater systems'.

A spokesperson for Hafren Dyfrdwy said the firm would 'ensure that we will not be the reason for any unhealthy rivers in Wales by 2030' and would be 'rapidly reducing' polluting spills.

Severn Trent said it recently announced a programme worth £1bn to reduce its impact on rivers to 'almost zero by 2030'.

Dŵr Cymru said it 'will not shy away from the challenges facing us'.