You can actually make sea water drinkable, by using a very simple technique called desalination (or desalinization / desalinisation) through distillation (a process of separating the component substances from a liquid mixture by selective vaporization and condensation). Info and a video:

You can use this technique in emergency situations or any other conditions where there is only a source of salt water.

The process to make sea water drinkable

1. Collect the salt water and put it in something where it can boil under fire or any other heat source capable to bring the water to boiling temperature.
2. Use your innovation to create or use something that can “collect” the steam from the boiling water, being capable to transport the steam particles (water) to another container.
3. You can consume safely the collected water, but wait for its temperature to fall, except if you need it to be hot.

A simple drawing to give you an idea:

Here is a video sample from Discovery, showing what you can do in an emergency situation: