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. You can consume the collected water safely , but wait for its temperature to fall, except if you need it to be hot.
If you boil the water and transfer the vapor to a different container, then the salt will be left behind in the first tub, whereas the freshwater will be in the other container. If you want specifics, then you can do the following:
Boil the salt water in a pot with a lid. Offset the lid slightly so that the water that condenses on the inside of the lid will run down the side to be collected in a separate container.
Once again, the salt cannot evaporate, so it is left behind in the pot as a solid.
