If you found yourself on a desert island, there is a good chance you could survive for many days with some quick thinking and a vessel made from a leaf or hollowed fruit. To turn salt water into drinking water or fresh water, one must rely on the principles of nature. When water evaporates, it leaves the salt behind and pure water is collected. The following process is based on the solar still method of collecting water for drinking in an emergency situation.
Dig a hole to collect water. The hold should be at least 1 m (3 feet) deep and wide enough for you to reach in. As you are nearing the bottom, you should see very damp sand, if not puddles of water. Take your time since you are limited on water and the exertion will cause you to need water sooner.
Place a vessel into the centre of the hole. The vessel can be a hollowed-out coconut, fruit or a leaf. If there is ample vegetation on the island, you can add vegetation to the hole around the vessel. Its water will evaporate and accumulate in the vessel.
Cover the hole and weigh down the cover. Place the fronds over the hole and cover it as completely as possible. Secure the outer edge with rocks. Place a few rocks at the centre of the cover to create a slight indentation where the vessel is. This will direct the water to the vessel. Over the course of the day and night, dew and condensation will gather on your makeshift cover and drop into the vessel.
Remove the vessel from the hole periodically to drink the water or to store it in other vessels for later use. Place the vessel back in the hole to continue to accumulate water. The water will be safe to drink. No purification is needed.
On future excursions, bring a plastic sheet with you. The plastic makes for a much more airtight cover that will gather water more quickly.