How to Make Salt Water Safe to Drink: Survival Desalination Explained

According to the UN, water scarcity affects more than 40% of the world's population, making knowledge of alternative water sources like desalination crucial. While undrinkable directly, there are multiple scientific methods to purify saltwater for consumption.

Quick Summary

Effective desalination processes like distillation, reverse osmosis, and solar stills can convert saltwater into a potable supply for survival or long-term use. Understanding the principles behind these methods is key.

Key Points

• Distillation Method: Boil saltwater and collect the pure, condensed steam to remove salt and impurities.

• Reverse Osmosis (RO): Use high pressure to force water through a semi-permeable membrane, leaving salt behind.

• Survival Solar Still: A low-energy, passive method for desalination using the sun's heat to evaporate and condense water.

• Never Drink Boiled Saltwater: Boiling water does not remove salt; it only increases its concentration, accelerating dehydration.

• High Purity Water: Both distillation and RO remove bacteria, viruses, and dissolved solids to produce clean drinking water.

• Choose the Right Method: The best desalination method depends on the scale, available resources, and urgency of the situation.

• Large-Scale Desalination: Modern reverse osmosis plants are used globally by coastal cities to address freshwater shortages, though they require significant energy and have environmental considerations.

Why You Must Never Drink Untreated Saltwater

Drinking saltwater is extremely dangerous to human health. When you consume seawater, its high salt concentration draws water from your body's cells, including the water your kidneys need to flush out the excess sodium. This leads to a cycle of accelerated dehydration, which can cause increased heart rate, nausea, vomiting, diarrhea, and, in severe cases, kidney failure, coma, or even death. Boiling alone is not a solution, as it will kill bacteria but leave the salt behind, making the water even more concentrated and harmful.

Method 1: The Distillation Process

Distillation is one of the oldest and most reliable ways to make saltwater drinkable. It mimics the natural water cycle by heating water until it evaporates, leaving the salt and other impurities behind, and then condensing the steam into pure, fresh water.

Simple Survival Distillation

For an emergency or survival scenario, a simple distillation setup can be improvised with a few basic items:

• Items Needed: A large pot with a lid, a collection cup or bowl, saltwater, and a heat source.
• Process:
  1. Place the collection cup in the center of the large pot, ensuring it is elevated and won't float in the saltwater. The cup must be clean.
  2. Pour saltwater into the pot around the cup, but do not fill it to the point where the cup could float or seawater could splash inside.
  3. Place the lid upside down on the pot. This creates a sloped surface for condensation to form.
  4. Put a small weight, such as a clean rock, on the center of the upside-down lid. This will cause the condensing freshwater to drip into the collection cup.
  5. Bring the water to a rolling boil and maintain it for at least 5 minutes to kill bacteria, ensuring the steam is captured and directed towards the cup.
  6. Let the setup cool completely before collecting and drinking the distilled water.

Solar Still Method

A solar still is a passive method that uses the sun's energy for desalination. This is particularly useful in sunny, arid regions.

• Items Needed: A container, clear plastic sheeting, and a small weight.
• Process:
  1. Dig a hole in the ground and place a clean cup in the center.
  2. Fill the space around the cup with saltwater, making sure the level is below the cup's rim.
  3. Cover the hole tightly with clear plastic sheeting and secure the edges with soil or rocks.
  4. Place a small rock on the center of the plastic, directly over the cup, to create a low point where condensate will collect.
  5. The sun's heat will evaporate the water, which will condense on the underside of the plastic and drip into the cup.

Method 2: Reverse Osmosis (RO) Desalination

Reverse osmosis is a modern, highly efficient method for desalination that is used on a large scale by cities and in compact portable units. Unlike distillation, it does not use heat but relies on pressure.

How RO Works

In an RO system, high pressure is applied to the saltwater, forcing it through a semi-permeable membrane. The membrane's tiny pores allow water molecules to pass through but block the larger salt ions, minerals, and other impurities. The result is purified freshwater on one side and a concentrated brine on the other.

Portable RO Desalinators

Numerous portable and manual RO units are available for marine or emergency use. These systems can be hand-pumped, powered by batteries, or use solar energy, making them invaluable for boats, off-grid living, and disaster relief. Modern RO units are increasingly energy-efficient, with energy recovery devices reducing power consumption significantly.

Distillation vs. Reverse Osmosis Comparison

Feature	Distillation (Thermal)	Reverse Osmosis (RO)
Energy Source	High heat, very energy intensive.	High pressure pump, lower energy consumption than distillation.
Technology	Mimics natural water cycle: evaporation and condensation.	Uses semi-permeable membranes to filter water molecules.
Portability	Improvised kits are portable, but inefficient. Large-scale thermal is not.	Highly portable units available for emergency and personal use.
Speed	Very slow due to heating, evaporation, and cooling time.	Generally faster than distillation for a given output, but dependent on system size.
Contaminant Removal	Removes nearly all contaminants, including bacteria, viruses, salts, and heavy metals.	Removes dissolved salts, chemicals, bacteria, and viruses, but additional filtration may be needed for some VOCs.
Initial Cost	Low for improvised systems; high for large industrial setups.	Higher initial cost for the specialized membrane and pump technology.
Water Taste	Can be bland due to mineral removal.	Can be improved with post-filtration remineralization.

Large-Scale Desalination Projects

Many coastal nations with limited freshwater reserves rely on large-scale desalination plants using reverse osmosis to provide drinking water for their populations. Countries like Israel and Saudi Arabia have invested heavily in these facilities to secure a steady water supply, although the process is expensive and energy-intensive. Large plants must also manage the environmental impact of brine discharge, ensuring it is diluted and dispersed properly to minimize harm to marine ecosystems.

Conclusion

While drinking saltwater directly is never an option due to severe health risks, several effective methods exist to transform it into safe, potable water. The choice between simple, low-tech solutions like a solar still and advanced, high-efficiency systems like reverse osmosis depends on the scale, urgency, and available resources. For survival situations, improvised distillation is a life-saving skill, while for consistent, high-volume production, modern RO systems are the leading technology. Understanding these processes is critical for preparedness and a vital tool in confronting global water scarcity. For more general water purification information, the National Park Service provides excellent resources on treating freshwater.

Frequently Asked Questions

Can you just boil saltwater to make it drinkable?

No, simply boiling saltwater will kill bacteria but leave the salt and minerals behind, resulting in an even more concentrated, dangerous liquid that accelerates dehydration.

How does a homemade solar still work?

A solar still uses the sun's heat to evaporate saltwater, causing condensation on a plastic sheet, which is collected as pure, distilled water that drips into a designated container.

Is desalinated water safe to drink long-term?

While safe from salt, desalinated water lacks beneficial minerals. For long-term consumption, remineralization is often recommended to improve taste and provide essential nutrients.

What is the most energy-efficient way to desalinate water?

Reverse osmosis is generally more energy-efficient than thermal distillation, especially for larger volumes. Modern RO systems often use energy recovery devices to further reduce power consumption.

Can a regular water filter purify saltwater?

No, standard water filters and purification tablets are designed for freshwater contaminants like bacteria and protozoa, not dissolved salts. A special desalination filter or RO system is required.

What are the main dangers of drinking saltwater?

The high salt concentration draws water from your body's cells, causing rapid and severe dehydration, kidney stress, nausea, and potentially death.

How do portable desalination units work for survival?

Portable units, often using reverse osmosis, are manually or battery-powered. They force water through a semi-permeable membrane to produce a small but critical supply of fresh water.