Water or Fire Damage
Water or fire damage sounds like the worst-case scenario in this catalog, and sometimes it is. More often, though, the platters or flash chips inside are better protected than the case around them suggests — and the instinct to dry the drive out and try it is usually what causes the real damage.
What's actually happening
Water and fire damage a drive in different ways. With water, the real threat is corrosion — anything but pure distilled water carries dissolved minerals that leave a conductive residue as it dries, bridging connections on the circuit board that should stay isolated. That process begins fairly quickly once a wet drive is powered on, or even just left to air-dry without control. The platters or flash chips themselves, sealed away from the electronics on many drives, can survive full submersion completely fine. With fire, direct flame reaching the storage media itself is usually unrecoverable, but far more common is smoke and heat damage to the case and circuit board while the sealed internal chamber of a hard drive stayed protected long enough underneath.
How recoverable this really is
For liquid damage, the outcome depends on the device, the liquid, contamination, corrosion, and whether power was applied. The important universal rule is not to power the device or improvise household drying or cleaning procedures. For fire damage, recoverability depends heavily on heat, deformation, soot, water used during firefighting, and whether the recording media itself was damaged.
The general approach
Disconnect power, avoid opening a hard drive outside an appropriate controlled environment, and transport liquid- or fire-damaged media for professional evaluation without trying to boot, heat, freeze, rinse, or repeatedly test it. Handling requirements differ between sealed hard drives, SSDs, phones, memory cards, and other devices, so preserving the device as received is safer than applying a universal wet/dry treatment.
Do not, under any circumstance, power on a drive that's been wet — not "just to check," not once it looks dry. And don't attempt to open, disassemble, or even wipe down a fire- or water-damaged drive yourself. Both mistakes cause far more permanent data loss in this scenario than the original water or fire exposure ever does.
Like the other physical-damage scenarios in this catalog, this is squarely on the hardware side of the software vs. hardware recovery tools line — no recovery software runs until the electronics are repaired, bypassed, or the media is safely extracted. This is also precisely the scenario the "somewhere physically separate" leg of a proper backup exists for — see Backup Drive Picks. Damage this physical is squarely cleanroom territory — see our directory of major physical recovery providers for labs equipped to handle it.
This page describes the general situation, not a guaranteed fix for your specific case. If you'd rather have someone experienced take a look before you try anything, see what a hands-on evaluation looks like.