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
- 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.
- 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.
- 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: