How does desalination work? Plan for water plant in Cornwall

Five public information events are taking place in July about the proposals, which the company says would “improve water resilience across the region.”

Desalination is the process of taking seawater and turning it into drinking water. You can read more about how this works below.

In May, South West Water announced plans to deliver its desalination scheme in two phases.

The first phase, focusing on the “pressing need to secure climate-resilient water supplies”, consists of providing a smaller desalination plant in Par, near to Restormel Water Treatment Works, using water from St Austell Bay.

This would be made up of approximately five shipping container-sized units, and use existing infrastructure to avoid any impact to the marine environment, including seagrass and maerl.

The company said a plant this size should be capable of producing between 2.5 and five million litres of clean drinking water daily when needed, and would allow more time to develop an application for a larger desalination plant - the second phase of the project.

How desalination works (Image: Getty Images)

South West Water previously met with locals in December 2023 to discuss its proposals for desalination, and is now holding three in-person public information events and two online sessions, ahead of submitting a planning application for the phase one plant later this summer.

The in-person events will be held in Par tonight (Monday, July 15) in Lostwithiel on July 17 and St Blazey on July 18, with two online sessions taking place on July 23 and 25.

Each event is designed to help South West Water develop its project with the community and local customers in mind, addressing concerns and taking on board feedback where possible.

What South West Water says

David Harris, South West Water’s drought and resilience director, said: “Desalination is one part of our wider £125 million investment plan to increase the water resources available in Cornwall by 45 per cent and in Devon by 30 per cent by 2025, to break the cycle of drought.

“Regulators are encouraging water companies to develop supplies that are resilient to the impacts of climate change, and desalination allows us to protect supplies across our region in the face of a changing climate in ways that more common interventions cannot.

“We share the passion that many locals have shown to protect the sensitive marine environment in St Austell Bay and this month’s events will provide us with an opportunity to continue demonstrating that we are doing everything we can to minimise any impact we have to marine habitats.”

How does desalination work?

The practice of desalination is explained in more detail on South West Water’s website.

It states the process begins by filtering the seawater to prevent marine life and any debris from entering the works. It then goes through a range of treatments to remove solid matter and filter the water to acceptable levels.

Dissolved salts are removed using reverse osmosis – a process of forcing water through tiny holes at high pressure, with the membrane catching the impurities and only allowing fresh water through.

The process of reverse osmosis in desalination (Image: Getty Images)

Important minerals are then added back into the water so that it matches the raw water quality at the treatment works.

Particles and solids previously removed are either recycled or returned to the sea, including the very salty water (brine) that remains after the osmosis process. This is released into the sea at deep water, to minimise the impact on the marine environment.

Where are the public events taking place?

The five public events will be held at:

Monday, July 15 – Cornubia Lower Hall, Par, PL24 2AQ – 4pm to 7pm

Wednesday, July 17 – Church Rooms, Lostwithiel, PL22 0BH – 4pm to 7pm

Thursday, July 18 - Alexander Hall, St Blazey, PL24 2JH – 6.30pm to 9pm

Tuesday, July 23 – Virtual webinar session – 6pm to 7.30pm

Thursday, July 25 – Virtual webinar session – 6pm to 7.30pm

To find out how to register to attend an event, or for more information on South West Water’s desalination proposals, visit www.southwestwater.co.uk/desalination