Written Statement: Boil Water Notice – Maerdy Water Treatment Works Incident

On 22 May, Dŵr Cymru Welsh Water issued a boil water notice affecting communities in Rhondda Cynon Taf, following an operational issue at the Maerdy Water Treatment Works.

The notice was issued as a precaution following an issue affecting the chemical dosing process at the treatment works. This was caused by a burst pipe feeding coagulant into the treatment process. While this meant the treatment process was not operating as intended, water continued to pass through the remainder of the treatment stages and was therefore only partially treated. This incident did not involve excess chemicals entering the water supply, as has been suggested in some commentary, but rather reduced effectiveness of part of the treatment process.

In response, Dŵr Cymru Welsh Water temporarily stopped water from entering the network and advised customers to boil tap water while the issue was investigated and resolved. Although the repair was completed within hours, water already within the system required further management, and the boil water notice remained in place until water quality had been fully confirmed.

The notice has now been fully lifted across all affected areas, following consistently clear water quality sampling, confirmation that the network has been fully flushed, and all supplies restored to the high standards customers rightly expect. The notice was lifted through a phased approach between Monday 25 May and Tuesday 26 May. The phased approach was deemed appropriate due to the size of the area affected and the time it took to allow fully treated water to move through the system and ensuring test results consistently confirmed that supplies met drinking water quality standards.

Customers can now use their tap water as normal for all purposes, including drinking, cooking and brushing teeth, and no public health advice remains in place.

I recognise the disruption this incident has caused to residents, businesses and public services, particularly during the recent period of warm weather, and I thank communities for their patience and understanding while the issue was resolved safely.

I would also like to thank Dŵr Cymru Welsh Water, Rhondda Cynon Taf County Borough Council, public health partners and all responding organisations for their coordinated and professional response, including support provided to vulnerable households and priority sites. During the incident Dŵr Cymru Welsh Water saw an increase in customers registering for their priority service. I would like to highlight the importance of this service to all customers who identify as vulnerable before an incident occurs.

Dŵr Cymru Welsh Water is providing compensation to affected household and non-household customers.

Payments will be made directly into customers’ bank accounts within 10 days where details are held, or by cheque where this information is not available. Household customers will receive £20 per day for the duration of the boil water notice, with non-household customers able to apply for appropriate goodwill payments where they have experienced additional costs or loss. Further information is available on the Dŵr Cymru Welsh Water website.

Dŵr Cymru Welsh Water has now moved into stand‑down and recovery, and bottled water stations were stood down at midday on 27 May.

Dŵr Cymru Welsh Water will undertake a post‑incident review to identify lessons and strengthen resilience and preparedness. This will be subject to independent scrutiny by the Drinking Water Inspectorate, which will investigate the incident and ensure that any necessary further action is taken.