Two-thirds of the Earth is covered in water, but only 2% of it is pure. Drinking seawater causes cells to release more water, leading to dehydration. The best way to extract fresh water from the ocean is through distillation. To distill water, heat sea water until it evaporates, then trap the evaporated water vapor until it cools and condenses back into liquid water, which will be free of salt and safe to drink.