Mermaid Quay | Dwr Cymru Welsh Water
Dwr Cymru Welsh Water
Mermaid Quay Sewer Upgrade

Mermaid Quay

Welsh Water is investing £2 million to upgrade the sewer system in the Mermaid Quay area of Cardiff Bay. The work is essential to make sure we continue to provide customers in the area with a first-class wastewater system they can rely on. This page provides an overview of the work and information on progress on site.

Work needed to be done following reports of local internal flooding caused mainly by the illegal discharge of fat, oil and grease (FOG) down the drains and other items such as wet wipes and cotton buds being flushed down the toilet that build up in the sewer and cause blockages. Frequent cleaning to clear the blockages can damage the sewer and that is what has happened here in Mermaid Quay.

The work which began on site in September 2018 involved carrying out repairs to the Victorian brick sewer which runs under Bute Street and also laying a new sewer pipe on Stuart Street. We have also had to do a lot of work removing fat blockages – also known as fatbergs - from the sewer along Stuart and Bute Street. This took longer than expected due to the poor condition of the sewer and the amount of blockages found. Between September and December we removed 800 tons of FOG, the equivalent of 133 African elephants.We have also had to make safe a number of collapses in the sewer by excavating them and constructing underground boxes to ensure the ground around the damaged sewer is stable.

Due to the issues encountered, we have had to revise our construction plan which aims to be less disruptive to the businesses and residents in Mermaid Quay. Our new plan involves installing a new sewer pipeline within the existing brick egg sewer and then filling the existing brick egg sewer with concrete.

This work will remove the need for us to build an underground pumping station as the sewer will operate using gravity and will not require a pumped solution. As long as everything goes to plan, we aim to complete the work by the beginning July 2019. Our team will work seven days a week to ensure that the work is completed on time. A timeline showing key milestones from when we came on site to the present day is shown here.

We have created a Frequently Asked Questions document to provide further information and hopefully answer any further questions you may have on the scheme.

We will continue to update local residents and businesses with a regular newsletter which will be available on this website. The latest one is here.

Phased Approach

The work will be carried out in a phased way to minimise the impact on the local area.
The original first phase of the scheme has been completed. This involved the removal of the temporary footbridge on Stuart Street, repairing the original Victorian brick sewer and removing FOG blockages in the area between Stuart Street and Bute Street. A new pipe was also installed inside the existing egg brick pipe along Stuart Street.

Within the new plan, new programme phases have been developed to provide an overview of different phases of the work needed to complete the work on installing a new new long term sustainable sewer in Mermaid Quay. An overview of each phase is shown here.

Want to know more?

Any updates will be available on this website by clicking to view our latest newsletter.

We also have a site office at 19A Bute Street. You are welcome to call in and see our Customer Engagement Officer, Tomos Davies for more information. The site office is open 5 days a week, Monday to Friday between 9am and 5pm. You can also reach Tomos on 07866818183 or Should you need to contact us urgently, you can call our wastewater team on 0800 085 3968.

Map of pedestrian access on Mermaid Quay