The Aircraft Carrier Alliance have published insight into how HMS Queen Elizabeth turns seawater into fresh water.
With the vessels designed around 9 month deployments, they require access to fresh water for their 700+ strong crew.
“To ensure the crew has a supply of fresh water while at sea, a £1 million reverse osmosis system draws in sea water and produces 540 tonnes of fresh water a day.
Reverse osmosis is the process by which high pressure is applied to saltwater, pushing it through a semi-permeable membrane. Due to the size of the salt molecules, only smaller water molecules can pass through the membrane, resulting in fresh water.
Three reverse osmosis plants have been providing the crew and industry workforce on board HMS QUEEN ELIZABETH with fresh water while the ship has been undergoing her maiden sea trials. This is the largest scale use of the system on a Royal Navy ship.
The reverse osmosis plants have the capability of taking in saltwater and transforming it into fresh water at a rate of 175mᶟ per day – enough to fill nearly 12,000 bath tubs – and will be enough to meet the demands of up to 1,600 embarked personnel. The fresh water produced and stored on board the Queen Elizabeth Class carriers each day will equate to approximately 175,000 litres, which is around six times the capability of a normal vessel. The water can not only be used for drinking, but for cooking, showers, dishwashers and general ship husbandry.
The three plants have been developed to run completely autonomously, requiring minimal input from the operating crew. The system is unique in that it can also dispose of the water used on board cleanly and safely through an additional filtration unit, which purifies the water on exit from the ship. This function could also be utilised in the future for humanitarian operations, delivering clean and filtered water to those in need of it.”
Engineering Technician (Marine Engineering) David Carey, is one of the crew members responsible for the ship’s fresh water and reverse osmosis plants:
“In the morning we carry out daily checks and also preventive maintenance on all of our equipment, to keep machinery running smoothly.” ET (ME) Carey told us. “For me, the major event after HMS QUEEN ELIZABETH sailed was the commissioning of the reverse osmosis plants which allow the ship to make its own fresh water.
This was achieved with the help of a company called Salt Separation Services, who helped to set the three reverse osmosis plants to work. It was a challenging task but now allows HMS QUEEN ELIZABETH to produce 540 tonnes of her own fresh water a day.”