You make salt water drinkable by removing the dissolved salt, a process called desalination. The simplest method anyone can use at home or in a survival situation is distillation: boiling the water, capturing the steam, and collecting it as it condenses back into liquid. The salt stays behind, and the condensed water is fresh. More advanced methods like reverse osmosis use high-pressure membranes, but distillation requires nothing more than a heat source and some basic equipment.
Why You Can’t Just Drink Salt Water
Seawater contains roughly 35 grams of salt per liter, about seven times what your kidneys can efficiently process. When you drink it, your body actually loses more water trying to flush the excess salt than it gains from the drink itself. This accelerates dehydration rather than relieving it. There is no safe amount of seawater to drink without processing it first.
Distillation: The Most Accessible Method
Distillation works because water evaporates at 100°C (212°F), but salt does not. When you boil salt water, only pure water vapor rises. If you capture and cool that vapor, it condenses into drinkable fresh water while the salt remains in the original pot. This is the same principle behind natural rainfall: the sun evaporates ocean water, leaving the salt behind, and the vapor forms clouds that produce fresh rain.
To distill salt water on a stovetop, you need a large pot with a lid, a smaller collection bowl, and ice. Fill the pot partway with salt water and place the collection bowl in the center, floating or propped above the water line. Invert the lid so it forms a dome shape pointing downward, then pile ice on top of the inverted lid. As the water boils, steam rises, hits the cold lid, condenses into droplets, and drips down into the collection bowl. This is slow but effective, and the water in the collection bowl will be salt-free.
The main limitation is output. You’ll use a significant amount of fuel (gas, electricity, or fire) relative to the small volume of water you collect. For a household emergency, this method can produce enough drinking water to keep you going, but it’s not efficient for large-scale needs.
Solar Stills: Distillation Without Fuel
A solar still uses sunlight instead of a stove to evaporate water. The simplest version is a hole in the ground lined with plastic sheeting. You pour salt water into the hole, stretch clear plastic over it, and place a small rock in the center of the plastic so condensation drips down into a container below. The sun heats the water, vapor rises, condenses on the cooler plastic, and trickles into your collection cup.
Ground-level solar stills are notoriously low-yield. Engineered versions perform much better. Research on stepped solar stills shows that a basic design produces around 3,600 milliliters per square meter per day, roughly 0.95 gallons. Adding features like corrugated surfaces to increase evaporation area boosted output by 54%, pushing production to about 5,500 mL daily. Designs incorporating wicking materials like jute cloth and preheated water reached 6,500 mL per square meter per day, nearly 1.7 gallons. These are purpose-built units, but the underlying physics are the same as a DIY version. A larger collection surface and better insulation will always improve your yield.
If you’re building a solar still for emergency use, prioritize a large, clear plastic sheet, a dark-colored basin to absorb more heat, and good sealing around the edges to prevent vapor from escaping. Output depends heavily on sun intensity, so expect significantly less on cloudy days.
Reverse Osmosis: The Industrial Standard
Most of the world’s desalination plants use reverse osmosis (RO). This method forces salt water through a membrane with pores so tiny that water molecules pass through but salt ions do not. For seawater, the pressure required to push water through these membranes reaches up to 1,000 PSI, about 15 times the pressure in a typical car tire. That enormous pressure is why RO systems need heavy-duty pumps and specialized equipment.
Portable RO units do exist for boats and emergency kits. Hand-pump models designed for survival use can produce roughly one to two liters per hour with sustained manual effort. They’re effective but physically demanding, and the membranes need periodic replacement. For home use, under-sink RO filters handle brackish water well, but most household units cannot process full-strength seawater. They’re designed for tap water with lower salt concentrations.
Boiling Alone Does Not Work
A common misconception is that simply boiling salt water makes it safe to drink. Boiling kills bacteria and parasites, but salt does not evaporate with steam. If you boil salt water in an open pot, the water evaporates into the air and the remaining liquid actually becomes saltier. You must capture the steam and condense it separately. The collection step is what makes distillation different from ordinary boiling.
Practical Comparison of Methods
- Stovetop distillation: Works anywhere you have a heat source. Produces small quantities, perhaps a liter per hour depending on your setup. Good for short-term emergencies.
- Solar still: No fuel required, but output is limited by sunlight. A well-built still produces 1 to 1.7 gallons per square meter per day. Best for sustained situations in sunny climates.
- Portable RO pump: Compact and efficient per liter, but physically tiring and requires replacement filters. Ideal for boaters and offshore survival kits.
- Home RO system: Handles mildly salty or brackish water but typically cannot desalinate full seawater. Not a substitute for distillation in a coastal emergency.
Tips for Better Results
Whatever method you use, a few principles improve your output. Dark containers absorb more solar energy and heat water faster. Insulating the sides of your still or pot reduces heat loss and keeps more energy focused on evaporation. Using a cooling mechanism on the condensation surface, whether ice on a pot lid or shade on the upper plastic of a solar still, increases the temperature difference between the steam and the collection surface, which speeds condensation.
If you’re distilling water for drinking, let it cool and taste a small amount before relying on it. Properly distilled water should taste flat and slightly “empty” compared to tap water because it lacks minerals. That flatness is actually a good sign: it means the salt was successfully removed. You can add a tiny pinch of table salt or mix in a small amount of untreated fresh water to improve the taste if you find it unpleasant, but the distilled water itself is safe as-is.
For long-term or large-volume needs, combining methods works well. Run a solar still during the day and use stovetop distillation in the evening to maximize your daily output without exhausting fuel supplies.