Survival at sea or when stranded on the beach or other areas were salt water is the only source of water can be very challenging. Because it takes 2 liters of water from your body to remove the amount of salt in 1 liter of seawater, drinking seawater will actually dehydrate you, resulting in illness and even death. There are techniques, however, they can be used to ensure that you drink clean and safe water.
Sea ice can be a useful source of fresh water. Look for ice that is crystalline and clear with a bluish color to it. This ice is naturally cleaned by the freezing process and has little salt in it. Do not use sea ice that is opaque or gray in color; it is much more likely to have a higher salt content.
Steam created from seawater is very low in salt. When on the beach, try digging a deep hole in the sand that will allow seawater to seep in. Build a fire and heat some rocks. Drop the hot rocks into the water. Hold a shirt or other cloth over the hole to absorb the steam, then ring the cloth out. The condensed steam will be clean water that you can then drink.
Below Ground Still
A below ground still uses the sun to produce condensation, which can then be collected for later use. Dig a sloping hole in the sand down to where the sand is wet but not seeping. Place a container at the bottom center of the hole. Insert a piece of tubing into the container that is long enough to reach from the container to above the edge of the hole. Cover the hole entirely with a sheet of clear plastic. Place sand, dirt or rocks around the edge of the hole to hold the plastic in place. Position a rock in the middle of the plastic sheet so that its lowest point is above the container. As the sun heats the still, water will evaporate and condense on the plastic sheet. This condensation will then run down the sheet and drip into the container, which you can then drink through the drinking tube.
Emergency desalter kits are available that can be used to clean salt from water. These can be purchased online or at Army Navy stores. Each kit contains chemical packets and a plastic container. When the container is filled with salt water and the chemicals are added, the salt is removed from the water. Each kit can produce up to 7 pt. clean drinking water.