Drinking from the sea

Published on POIS Helen Frank (author), ABIS Jarrod Mulvihill (photographer)

Location(s): Mallacoota, Vic

Topic(s): HMAS Choules (L100), Operation BUSHFIRE ASSIST

MV Sycamore conducts a rendezvous with HMAS Choules, right, during Operation BUSHFIRE ASSIST 19-20. (photo: ABIS Jarrod Mulvihill)
MV Sycamore conducts a rendezvous with HMAS Choules, right, during Operation BUSHFIRE ASSIST 19-20.

Surrounded by water but not a drop to drink. Where does a Royal Australian Navy ship get its drinking water from?

HMAS Choules’ water making capability was recently tested when the ship evacuated 1100 people from Mallacoota during Operation BUSHFIRE ASSIST 19-20.

Choules’ Engineering Officer, Lieutenant Commander Darrel Wolter said the ship could make a substantial volume of water for its own needs and more.

Choules can make more than enough water each day to meet our requirements, and can store a far greater volume on top of that,” Lieutenant Commander Wolter said.

“If we needed to, we could also transport water ashore.

Choules has the unique capability to be able to fill tankers and then transfer them ashore,” he said.

Most Navy ships employ a phenomenon called reverse osmosis to turn the saltwater they sail through into fresh drinking water.

Osmosis is the process of water moving from an area where it is relatively pure, across a semi-permeable membrane, to an area where the water contains impurities such as salt. The process is passive and therefore doesn't require the input of energy.

To reverse this process and make fresh water, energy is applied to the saltier water. This energy pushes the water through the membrane, leaving the salt behind and therefore desalinating the water.

Reverse osmosis can remove up to 99% of salts, particles, organics and bacteria from sea water.

Choules has two reverse osmosis (RO) plants, which can each produce up to 60,000 litres of drinking water per day.

The daily usage of water on board Choules is approximately 37,000 litres.

With 1100 evacuees on board, the daily usage peaked at 67,000 litres, but with a total capacity for 1.5 million litres: there was still plenty to go around.

Operation BUSHFIRE ASSIST 19-20 imagery is available on the Defence Image Gallery: