First thing's first – MacBook's aren't designed to be waterproof! High specification components and water really don't ever mix well together, and if the MacBook has been dropped into a bathtub, pond, or any other body of water where it's been submerged – even for just a second or two – it's most likely a goner.
Of course there's no reason why you can't follow the guide below to at least try and see if by some act of god it comes back to life, but you really need to expect the worst. So for the nature of this guide we're looking at what to do if you have spilt some liquid over the computer – when you might at least have a chance of saving its life.
Shut down electricity flow & the MacBook itself
Sure, you're going to be panicking once that water/tea/beer has been spilt over the MacBook, but in the worst case scenario it can at least be replaced. You, on the other hand, cannot, so we need to remove any risk of electrocution by switching off any supply. Before doing anything else stop the flow of electricity to the machine – turn it off at the socket, and hold the power button for a couple of seconds so that it instantly turns off. Forget the data – time is of the essence here.
Remove any accessories
Forget about worrying about ‘dismounting' and such; unplug any external components such as mouse, keyboard, hard drives, USBs etc. We don't want to run the risk of the liquid damaging these too, so quickly pull them out.
Flip & dry
Now for the most important part. Ideally we will be at this stage within seconds of the spillage but we now need to turn the MacBook over to reduce the risk of the liquid seeping deeper into the machine. This is especially true in the case of major spillage over the keyboard as this is where water is going to find it easiest to penetrate through.
Find a cotton or paper towel and try to soak up the liquid, carefully padding between keys and being sure to have the computer at an angle where liquid isn't going to seep towards the screen. If you have the right tools you can try to take the MacBook apart to dry the components individually but for the sake of uniformity let's assume that we don't (people have written books about taking Mac's apart!).
Hopefully most of the water will have been soaked up or expelled from the computer by now, yet the bad news is that plenty of those expensive components are likely going to be rather wet still. This stage is crucial if there's likely any possibility of saving the Mac.
Find an item that has plenty of gaps to channel airflow – plastic crates are ideal, clothes drying stands and even a shelf removed from the fridge might do. Lay a cotton towel over the top of the item and lay the MacBook open and face down upon it, with the screen at an angle hanging over the side. Position a fan underneath this box and turn on to full blast at a slight temperature (not warm/hot as you may fry the components rather than dry them).
Leave for four days. Yup four days…..
The reason it needs so long is that even the slightest patch of damp may be enough to finish off the MacBook when you power it up.
Turn it on? Or take to a specialist?
You need to be sure that there's no water left inside. Feel free to try turning it on or, alternatively, take it to a repair store and get their opinion. There's a good likelihood they will be able to give you a fair opinion if there's a chance of resurrecting it.
Once powered up you should be able to tell if/how badly the computer is damaged. Check the keyboard, memory, display, hard drive etc. Even if by a miracle the Mac seems fine, now is the time to back up any important files to the cloud or external hard drive as water damage can take a while to manifest and can limit the lifespan of the computer.
If it's damaged, won't turn on or is beyond practical use consider getting in touch with Apple for advice. Likely they may charge as much as its worth to repair or replace broken components but all is not lost.
There are many smaller private companies that offer repair services for a fraction of the cost. If you do consider using a private company, then check online as many of these companies have websites such as FixAppleNow.com who are based in Miami. It may also be advisable to ensure which ever company you trust with your MacBook repair, they are experienced Apple certified technicians who will be using Apple OEM parts, rather than using cheaper and inferior parts. It may save money in the short term, but by using original parts where possible should ensure you do not have further problems with your MacBook in future.