Finding a source of potable water is one of the top priorities in any survival situation, but this is especially challenging in coastal areas, on small islands, or at sea. Drinking seawater is extremely harmful to your body as a result of its high level of dissolved salts, and boiling seawater will only concentrate its salt content. The most practical method of processing seawater into drinkable fresh water is distillation.
Distilling water traps pure steam as condensation, while excluding minerals such as salt. Since distillation is accomplished boiling the water, it's also an effective method of destroying harmful bacteria, protozoan cysts, and viruses that may be present in the water. For more information on the waterborne pathogens seawater contains, refer to our article “Debunked: Preventing Infection by Rinsing with Seawater”. Distillation can even be used to produce drinkable water from urine, unlike most other filtration and purification methods which cannot remove the dissolved salts.
When we think of distilling water, we often envision the large copper stills and networks of coiled tubes used to produce alcohol. These would provide an ideal way to distill water, but it's unlikely you'll have access to such equipment, especially in a survival situation. Fortunately, it's possible to distill water in smaller quantities using scavenged items.
In the following video, YouTuber NightHawkInLight shows how to distill water using two standard-sized glass bottles. He also adds metal trays and some sand to help act as heat sinks — this keeps the hot side evenly-heated and dissipates heat from the cool side. However, these additions aren't strictly necessary. Check out the full video below: