Llwyn-onn Water
Treatment Works

Cwm Taf Water Supply Strategy

Investing in new and resilient water treatment works and associated facilities which will provide our customers with a safe, reliable supply of clean drinking water for decades to come.

Welcome to our consultation

30th October – 10th December 2025

The information on this consultation site outlines our proposal to upgrade our existing Llwyn-onn Water Treatment Works in Bannau Brycheiniog National Park, along with water storage facilities and new pipeline networks.

Once upgraded these new facilities will also replace the existing Cantref Water Treatment Works, which will be decommissioned.

This is a statutory pre-application consultation and is designed to share with you the need for the investment, our proposals, draft planning application documents, and receive your feedback ahead of us submitting out planning application to the relevant local planning authorities – Bannau Brycheiniog National Park and Merthyr Tydfil County Borough Council.

We’ve created a virtual consultation room where you will find information about the proposal and how you can provide your views. Please make sure you visit the additional information on the main table within the virtual room and provided on the screens.

A separate virtual consultation room is available for our proposed Dan-y-Castell Water Treatment Works and Pontsticill Pumping Station: dwrcymru.com/danycastellproposal

Click here for a guide to the technical documents below.

Have your say

We want to hear your views.

Please take the time to read our consultation materials and then complete our forms to share your feedback.

There are separate forms for each proposal so we can ensure that any feedback received will be specific to each proposal. We have colour coded the forms for clarity. We welcome and encourage feedback on both proposals, for those who wish to comment on both you will need to complete the two feedback forms.

If you are unable to respond via one of the above channels, please call us on 0800 052 0130 to discuss alternative ways of sharing your feedback. (General enquiries 8am-6pm Mon-Fri, 9am-1pm Sat).

The closing date for responses is 23:59 on Wednesday 10th December 2025.

Your feedback is important to us. The feedback received as part of this consultation will be taken into consideration as we finalise our application. The comments raised, and how we considered them, will form part of our final planning application submission - set out in the Pre-application Consultation Report.