The Menai Data Centre: At What Cost?

Water, cooling, PFAS and the questions that still need answering

A massive new data centre is proposed beside the Menai Strait. We think some important questions still need answering.

A major data-centre campus is proposed on and around the former Ferodo site at Griffiths Crossing, near Caernarfon.

The planning application, C25/0740/20/EIA, was submitted by Gwelyfenai Ltd. It is an Environmental Impact Assessment application covering the demolition of existing structures, regrading of the site and construction of data-centre buildings together with generators, plant, substations, drainage and associated infrastructure.

The proposed site is approximately 41 hectares. The plans show up to five substantial data-centre buildings, with the tallest building exceeding 30 metres. The proposed electricity connection is rated at 450MW.

This is not a small development.

Up to 12 million litres of water a day?

According to the information reported from the Environmental Statement, the proposed data centre could require a maximum of approximately 11,949,120 litres of water per day.

That's nearly 12 million litres every day.

The developer has subsequently clarified that this is a maximum-use scenario rather than its expected normal daily requirement. It says the most likely requirement, based on the cooling technologies currently being considered, is approximately 700,000 litres per day.

That distinction is important.

Seven hundred thousand litres is very different from twelve million.

But twelve million litres is still a figure that appears in the environmental assessment, and we believe residents are entitled to understand exactly what it means.

What happens if the facility reaches its maximum operating scenario?

What happens during periods of particularly high temperatures?

What happens as the campus expands?

And how secure is the water supply over the lifetime of a development designed to operate for decades?

These aren't hypothetical questions about data centres generally. They are questions about the figures appearing in the documentation for this particular proposal.

What happens to the water afterwards?

Water consumption is only half of the issue.

Some cooling systems use water which is subsequently discharged as wastewater. Other systems can substantially reduce water consumption by recycling water through closed loops or using different cooling technologies.

The UK Government's National Framework for Water Resources 2025 specifically identifies data centres as a sector that can require large quantities of water for cooling.

It says water availability needs to be considered when data centres are planned, including the water requirements of the cooling technology selected and the location of the facility. It also notes that closed-loop systems are more water efficient than open-loop systems.

The Welsh Government has similarly acknowledged that there is significant variation in water consumption between different data-centre designs and has specifically referred to technologies such as closed-loop water systems as a way of reducing water use and waste.

So the choice of cooling technology matters.

And that is one of the areas we want more information about.

Dŵr Cymru has raised concerns

This isn't simply a concern being raised by local campaigners.

Dŵr Cymru Welsh Water has raised concerns about the proposal, including issues relating to the capacity of the local sewerage infrastructure and the information available about cooling technology and water requirements.

That deserves attention.

If a development potentially uses hundreds of thousands and under some scenarios millions of litres of water each day, the question isn't simply whether water can reach the site.

We need to understand:

Where is the water coming from?

How much will be consumed?

How much will enter the sewerage system?

Does the existing infrastructure have sufficient capacity?

What happens during extreme weather or peak demand?

And importantly, what safeguards will prevent additional pressure being placed on the environment?

Then there is PFAS

There is another issue which we think deserves much more attention: PFAS — per- and polyfluoroalkyl substances, often described as "forever chemicals".

There is now published scientific research showing that PFAS can be relevant to some advanced data-centre cooling technologies.

A peer-reviewed study published in Nature in 2025 examined the environmental impacts of different cooling technologies across the lifecycle of data-centre infrastructure.

It found that two-phase immersion cooling can support very high power densities but uses PFAS-containing fluids. The study also discusses the regulatory scrutiny surrounding PFAS and the potential environmental implications of accidental releases.

That is precisely why we think the Menai proposal should tell us which technology is actually being proposed here.

Why does this matter at the Menai?

Location matters.

The proposed development is immediately beside the Menai Strait.

The Menai Strait is environmentally important, and Dŵr Cymru is already carrying out work intended to improve water quality in the Strait. The Strait forms part of the Menai Strait Marine Special Area of Conservation.

That doesn't mean the data centre will pollute the Strait.

It means that any large development involving substantial water use, wastewater, industrial chemicals and cooling infrastructure needs to demonstrate that appropriate safeguards are in place.

If PFAS-containing cooling fluids are proposed, we want to know.

If they aren't proposed, we want that confirmed.

If PFAS-free alternatives are available and technically suitable, we want to know whether they have been properly considered.

So what have we asked for?

We have requested further information about:

• the precise cooling technology proposed;

• normal and maximum water consumption;

• the source of the water supply;

• how much water will actually be consumed;

• how much wastewater will be produced;

• whether the local sewerage system has sufficient capacity;

• what substances will be present in wastewater;

• whether any PFAS-containing substances will be used;

• the proposed cooling fluids and refrigerants;

• arrangements for preventing leaks and accidental releases;

• monitoring arrangements;

• disposal of cooling fluids and equipment;

• and whether PFAS-free cooling technologies have been assessed.

These seem like reasonable questions for a development of this scale.

This is about getting the facts right

The Menai Data Centre is being presented as an opportunity to regenerate a major former industrial site and bring investment and skilled employment to the area.

But large developments come with large responsibilities.

The Welsh Government has already acknowledged that AI and data-centre development could increase demand for water, while the UK's national water-resources planning recognises data centres as an emerging source of significant water demand.

Meanwhile, scientific research is already examining the environmental consequences of different cooling technologies, including the potential use of PFAS-containing fluids.

And Dŵr Cymru has raised concerns about infrastructure associated with this particular proposal.

We need the evidence.

We need to know exactly what is proposed, how much water it will require, what cooling technology will be installed, what happens to the wastewater, and whether any PFAS-containing substances will be involved.

We have requested more information.

And we will continue to ask for the answers.

Before a development of this scale is built beside the Menai Strait, the public should know exactly what it will take from the area and what safeguards will be put in place to protect it.