Chlorine and salt leave deposits that keep corroding long after the device feels dry.
What to do first
Speed matters more than technique. Power the device down, keep it upright so gravity pulls liquid away from the board, and resist the urge to test the speaker until the outside is dry.
How the tool helps here
Once the outside is dry, a low-frequency ejection cycle pushes trapped droplets back out through the speaker opening before minerals in the water dry into a film.
Try the free speaker cleaning tool and measure the result before and after.