When stranded, removing salt from seawater is crucial for survival as drinking saltwater is harmful. Based on methods used to remove salt, saltwater can be made potable through processes that separate the water from the salt. The primary methods mentioned for removing salt from seawater are distillation and reverse osmosis (RO).
Desalting Methods for Stranded Situations
While traditional filtering removes particles, removing dissolved salt requires more sophisticated techniques like distillation or reverse osmosis.
1. Distillation
Distillation is a process that mimics the natural water cycle. It involves heating saltwater until it evaporates, leaving the salt behind. The resulting water vapor is then collected and condensed back into liquid, which is pure, fresh water.
- How it Works:
- Saltwater is heated (by sun or fire).
- Pure water evaporates as steam.
- Steam rises and is cooled by a surface.
- Condensed steam (freshwater) is collected.
- Salt and impurities remain in the original container.
- Feasibility When Stranded: This method is relatively feasible even with limited resources. A simple solar still can be constructed using basic materials found or improvised in a survival scenario (like plastic sheeting, a container, and a weight). This process is powered by the sun.
2. Reverse Osmosis (RO)
Reverse Osmosis (RO) is a technological process that forces saltwater through a semipermeable membrane under high pressure. The membrane allows water molecules to pass through but blocks salt and other dissolved solids.
- How it Works:
- Saltwater is put under significant pressure.
- Pressure forces water through a specialized membrane.
- Pure water passes through, leaving salt behind.
- Feasibility When Stranded (Based on Reference): As noted, RO requires specific equipment: "RO requires that the source water be under pressure; so if you were stranded on a large enough vessel, with a generator and a pump you could use RO." This indicates that RO is generally not a viable method in typical "stranded" survival scenarios without access to significant power sources and specialized machinery like a generator and pump, usually found only on larger ships or facilities.
Comparing Desalting Methods
Here's a quick comparison of the methods mentioned in the context of being stranded:
| Method | Principle | Equipment Needed (according to reference) | Feasibility in Resource-Scarce Stranded Scenario |
|---|---|---|---|
| Distillation | Evaporation & Condensation | Basic setup (can be improvised like a solar still) | High (using improvised methods) |
| Reverse Osmosis | High-pressure membrane filtration | Pressure system, generator, pump (requires large vessel) | Low (unless on a suitably equipped vessel) |
Practical Considerations
If stranded, your ability to desalinate water will depend heavily on your location and available resources.
- Solar Still: On land or a life raft with materials, constructing a solar still is often the most practical method based on the principles of distillation.
- RO Systems: Unless you are stranded on a large, functioning vessel equipped with the necessary power and RO machinery, this method is likely unavailable. Portable hand-pump RO systems exist but are specialized equipment unlikely to be available spontaneously.
In summary, while stranded, focus on methods based on distillation principles, such as building a solar still, as reverse osmosis typically requires complex equipment that would not be available in a survival situation off a large vessel.
