Pure water is nearly harmless to electronics that are switched off. Tap water, flood water, coffee and seawater are not pure, and they leave salts and minerals on the board that draw moisture from the air and keep corroding copper long after the surface is dry. Powering a wet board is worse still: current flows where it should not, through the residue, and components short. A drive that was under water for an hour and never powered is a good job. A drive that dried out for a week and was then plugged in to see is a harder one.
On the bench a wet board is cleaned properly, ultrasonically where needed, inspected under magnification, and repaired where corrosion has eaten a trace or a component. Then it is powered once, in its diagnostic state, and imaged. On a soldered Mac or laptop the same cleaning and repair applies to the whole logic board, with the added constraint that the board itself has to run for encrypted storage to unlock; there is a page on soldered SSDs.
Heat is a different injury. Flash cells hold charge, and heat lets that charge drift, so a drive that spent its life at high temperature reads with more errors than one that did not. A short, intense heat, a fire, can kill the controller and blister the board while leaving the flash readable. A long, moderate heat, a laptop on a duvet for years, wears the flash quietly. Either way the drive is imaged once, with the weak pages retried carefully, and nothing else is asked of it.