Dŵr Cymru Welsh Water has submitted their planning applications on the Cwm Taf Water Supply Strategy that will secure reliable drinking water supplies for communities across south Wales for decades to come.

Planning applications have been submitted with Merthyr Tydfil County Borough Council and Bannau Brycheiniog National Park Authority which propose new water treatment facilities in the Merthyr Tydfil area and National Park.

If approved, the new facilities will replace the water treatment works at Pontsticill and Cantref, and upgrade the Llwyn-onn Water Treatment Works - facilities that have been serving the region for more than a century and are now becoming increasingly difficult and costly to maintain.

The £600 million scheme is the largest water infrastructure project in Welsh Water's history - the major upgrade will modernise treatment facilities and help ensure a safe and dependable drinking water supply to over 400,000 properties.

It will serve communities including essential services such as hospitals and schools, in Merthyr Tydfil, surrounding towns and parts of Cardiff.

The once-in-a-generation investment plans include:

• Construction of a new water treatment works at Dan-y-Castell Farm, Merthyr Tydfil, including treated water storage capacity, a new pumping station at the existing Pontsticill site and new pipelines connecting the facilities to the existing water supply network.
• Upgrades to the existing Llwyn-onn Water Treatment Works facilities, including additional water storage capacity and new pipelines connecting the facilities to the existing water supply network.
• The future decommissioning of the existing treatment works at Pontsticill and Cantref.

The plans have been developed following consultation with local communities and stakeholders, integrating the feedback to develop a sustainable solution by prioritising the use of previously developed land at existing sites. It includes design features such as green roofs and proposes long-term management plans to create species rich habitats and improving connectivity to meet Net Benefit for Biodiversity.

Roch Cheroux, Chief Executive of Dŵr Cymru Welsh Water, said:

“The project represents one of the most significant investments in Welsh Water infrastructure for generations and will help provide a safe, reliable and sustainable drinking water supply for customers for decades to come.

“As a company we need to deliver this critically important infrastructure for the benefit of our customers. The effects of climate change are already being realised in Wales, with extreme weather bringing more frequent storms and heatwaves, all increasing the pressure on our ageing water treatment assets.

“Submitting the planning application is an important milestone as we move forward with preparations for this major project, and once again will give the community and stakeholders an opportunity to comment on the plans.”

Feedback from the consultation has highlighted the importance of creating opportunities for local businesses through supply chain contracts, while supporting skilled jobs and apprenticeships during construction and delivery.

To help maximise supply chain opportunities, Dŵr Cymru Welsh Water is hosting a major supplier engagement event on 10 November 2026 at ICC Wales, Newport. The event will bring together potential suppliers, current delivery partners and businesses from across the wider supply chain to explore how they can contribute.

Welsh Water has already invited infrastructure investors, lenders and engineering partners to engagement sessions to help shape the commercial and procurement approach before formal procurement begins under regulator Ofwat’s Direct Procurement for Customers (DPC) model.