Thank you for your response. However, I am currently quarantining so I don't have the tools to open the laptop up and carry out your fixes. Will the device be broken for good then? 

Immediately power off, remove the base cover and disconnect the battery.  Then check for signs of water inside the system, and thoroughly dry the inside of the system.  Anything that showed water should be cleaned with 91% alcohol.  Once it's completely clean and dry, reapply power.  See if the system will power up.

DO NOT simply let the water dry - this will wind up producing corrosion.  Clean with alcohol and dry thoroughly.

If the system seems to power up but the screen remains black, see if there's even a faint image on the screen.  If there is, you've likely fried the power rail to the backlight - meaning a replacement system board is in the near future.

If you need a service manual link, post the full model number (inspiron 5421, 5479, etc.).

That can't be answered without an internal examination to look for and clean up traces of water, but the symptoms you've described are those of a blown-out backlight power circuit.  If the mainboard needs to be replaced, you're probably looking at a minimum of 50-60% of the initial system purchase price just for the part.

Left inside, the water damage will propagate, so clean it up as soon as possible.

Okay, I'll try to get it sorted asap. Thank you for your help.