Thousands of people across parts of south Wales were told to boil their tap water before drinking after Welsh Water identified a problem at one of its treatment works earlier this morning. Dŵr Cymru issued the boil water notice after detecting an issue with the chemical process used to treat drinking water at its Maerdy Water Treatment Works during routine checks.

The company said the notice applies to Blaenllechau, Bryngolau, Cymmer, Dinas, Edmondstown, Ferndale, Hopkinstown, Llwyncelyn, Maerdy, Tylorstown, Penrhys, Pontygwaith, Porth, Pwll Gwaun, Pantygraigwen, Treforest, Trebanog, Rhiwgarn, Tonyrefail, Tyn Y Bryn, Trehafod, Wattstown, Williamstown and Ynyshir. Residents in those areas were told to boil tap water before using it for drinking, brushing teeth, preparing food or making ice.

Welsh Water said customers would continue receiving water supplies and that no interruption to service was expected. The company temporarily stopped water from the site entering the network while investigations and remedial work continue. Text messages were being sent to impacted customers, residents could check whether they were affected using Dŵr Cymru’s online postcode checker, bottled water stations were being established and bottled water would be delivered directly to vulnerable customers registered on Welsh Water’s Priority Services Register.

The warning covers multiple communities in south Wales, including several in the Rhondda area and nearby places, and it lands at a moment when households need immediate guidance on whether the water coming from their taps is safe to use without boiling. Dŵr Cymru apologised for the disruption, but the company’s next task is clear: keep supplies flowing while it fixes the treatment issue and confirms when the boil water notice can be lifted.