It depends on what you mean by regular user. The process is quite simple: you just unsolder the old port and then solder a new one. There are plenty of instructions. Just make sure that you follow the instructions.
In this case, the PCB controller might be dead for some reason. Try to extract the hard drive itself and reconnect it using some adapter (the PCB from another ext hard drive will do just fine), but it might void your warranty. If the information is not that important, go for a warranty replacement.
Most likely you'll have to replace your keyboard. The danger of water lies mostly in dissolving of contacts, snd shorting them between each other. This may be the case, and it is too costly to redo all the wiring.