Although hard drives are not completely sealed, they only have a couple of small breather holes which are rarely breached by water. In most cases the external electronic parts (pcb) of the drive receive most of the damage. These parts are not well-protected as they are screwed to the outside of the drive. Salty or dirty water is particularly damaging to electronic contacts if not dealt with quickly.
Flood Damaged Hard Drive Problems
In a flood, the controller board electronics could be drenched in dirty water. If the machine was powered on at the time, it will be shorted out which could damage the circuit board. Time is quite critical with water damage, as the electronics must be safely cleaned to prevent corrosion taking hold. This must be done using a type of alcohol that won’t cause more damage. General cleaning products must not be used. If the hard drive was only submerged for minutes or hours there’s a good chance the water would not have reached the inside of the disk. If the inside of the disk did get wet then it needs an extremely careful cleaning procedure which is carried out in a controlled air environment (cleanroom). It will be important to leave no residue on the discs to allow the heads to fly properly.
Flood Data Recovery
If the corrosion on the PCB was severe we would try to read any crucial code from the remains of the circuit board and then write that to a replacement part. If the board cannot be read at all we would need to attempt to rebuild a new board using similar drives as a reference. In virtually all modern hard drives it is not possible to swap a circuit board without first adapting it. In some cases the information on the board is completely unique and critical for access to the data; Without the original board contents, a recovery may be either impossible or very time consuming.
If we are able to get the electronics working again, we would need to check the internal parts of the disk for damage. If possible we would need to repair any damage. We have recovered data from drives that have been underwater for days, and the water rarely causes severe enough damage to prevent recovery.
Fortunately most hard drives are buried inside a computer so get some added protection from there, at the expense of the computer taking the most damage.