Just an important bit of context: Water doesn't damage most electronics, especially not the solid-state hardware in a modern computer.

What does damage is short circuiting the electronics, which water can do.

As long as you cut power ASAP, remove and dry the battery (the most water-sensitive part of most computers), and make sure that everything is 100% dry before powering it back on again, you should be good, no matter how wet things got

This assumes that your electronics are wet with water. If you poured something more sinister into your computer, like sugary soda or beer, you probably need to rinse things off with alcohol and distilled water (therefore making things a LOT more wet) before drying it out and powering it back on.

The caveats are:

• LCD screens: they have lots of layers. Water between layers should be avoided if at all possible, as it will likely degrade the picture quality.
• Optical drives: moving greased parts with high precision optics and microscopic tolerances. Any dissolving of lubricant or deposition of residue could compromise the function of the drive.
• Hard Drives: should be sealed quite well with inert gas, but if any water gets in, it will fail catastrophically and will require disassembly for any chance of data recovery.
• Batteries: They can't be turned off, and can explode if shorted out.
• Oils: if you spill oil into a computer, it probably won't short anything out (depending on the oil), but you're going to have to completely take whatever you dumped oil into apart and meticulously clean it with a toothbrush and dish soap.