So true.. The USN washes aircraft with fresh water once a week ashore and aboard ship. I don't know what the interval is for the PLAN.
slight correction Gerry, when on land based rotation they can be washed every 2 weeks but out to sea definitely EVERY week w/o failed during maintenance inspection. As to PLAN, one would presume same schedule once it's all operational. Anything longer than a week at sea w/o washing would severely degrade aircraft integrity and flight safety due to corrosion and other environmental impact
With the sensitive skins of F-35s I would imagined such maintenance would be even more robust and taken with greater care since stealth integrity is now a factor unlike 4th Gen fighters.
Catapults takes up a LOT of water so CV17 etc would thereotically use a LOT less together with a smaller crew size but not sure how efficient or voluminous the desalination plant is onboard.
Sometimes pilots would purposely fly into a rain spell to 'wash' their planes like a free wash.
Below is a non-classified Aircraft CLEANING AND CORROSION CONTROL manual as published by NAVAIR for United States Navy aircraft.