How to Purify Salt Water: 4 Methods That Work

A whopping 70% of Earth’s surface is covered by water, but most of this is saline ocean water, which is non-potable and thus unsuitable for human consumption.

Yet, this doesn’t mean we can’t tap into this resource; quite the contrary! And this is what we’re going to talk about today: the actual, field-tested methods for purifying salty water and turning it from something harmful into something we can drink.

So let’s jump right into it and see how to an water into refreshing, life-saving drinkable water.

WARNING: You should never drink saline water!

Drinking saltwater straight from the ocean will cause fatal kidney failure. With an average salinity of 35,000 PPM (Parts Per Million), ocean water is drastically above the EPA secondary standard and WHO guidelines.

Those guidelines suggest that water below 500 PPM to 1,000 PPM is safe and acceptable for human consumption. Drinking raw saltwater will only accelerate dehydration and shut down your organs.

Before I explain the fine details of desalination, let’s put things into perspective. What if you find yourself stranded near the coastline or out in the open sea with no fresh drinking water within reach? The only viable option is to purify the ocean water yourself. Let’s learn how to do it.

Modern Reverse Osmosis (RO)

Portable, hand-cranked, or solar-powered Reverse Osmosis devices are the gold standard tooday for maritime prep and coastal survival.

Devices like the QuenchSea or Rainman force seawater through a microscopic membrane using human kinetic energy, producing up to a few liters of fresh water an hour.

I always keep a manual RO pump in my coastal emergency kit because it takes the guesswork out of the equation entirely and it is, by far, the easiest and most convenient method – as long as you can prepare in advance for it (and you should!)

Also read: How to Purify Water with Bleach

Solar Still: Plastic Bottle Design

A common method to generate fresh water from salty seawater is solar distillation. It’s a mobile and sustainable approach requiring nothing more than the sun’s heat to distill the water.

It might take a bit longer than other methods, but the simplicity and minimal effort needed to set it up make it a perfect option when you are in need.

This works specifically well in hot climates – for example, if you’re stranded on a deserted island with the tropical sun blazing overhead. Let’s see what you need to make drinking water using the solar still method.

What You’ll Need:

• One large plastic container (like a 1-gallon milk jug or a 2-liter soda bottle with a lid)
• A smaller plastic container that fits inside the larger one (like a water bottle or a 20oz soda bottle)
• A cutting tool (a knife, a sharp stone, or even a torn soda can)

Steps to Build the Solar Still for Purifying Water

1. Cut the bottom off the larger plastic bottle, then fold it under and inwards to create a trough to catch condensation.
2. Cut the top off the smaller plastic bottle to serve as the holding vessel for the saltwater.
3. Place the filled holding vessel in a spot with direct sunlight.
4. Cover the holding vessel with the larger catch vessel, ensuring a tight seal.
5. Place the still in the sunlight and wait for several hours.

Water will evaporate from the small bottle, it will hit the walls of the larger container and then, through condensation, it will turn back into safe to drink water.

After setting up the stills, find shade and rest. After a few hours of sun exposure, you should have fresh drinking water in your catch vessels.

Remember, in survival scenarios, any hydration is a lifeline, but don’t expect this method to produce tons of water – unless you have plenty of stills set up or very large containers.

Ideally, you will complement this setup with other passive collection methods like wrapping a plastic bag over foliage to collect plant transpiration.

The ‘Hole in the Ground’ Solar Distillation Technique

This method requires fewer materials than above, although it’s not an ideal situation. But we’re talking about survival here and anything can help.

This method essentially mimics the natural water cycle but on a much smaller scale. Sunlight warms the saltwater in a hole, creating vapor, which then condenses on a plastic sheet above and drips down into your catch vessel as pure water.

Gear You’ll Need:

• Digging tool (spoon, stick, piece of glass, aluminum can)
• Non-absorbent cover material (clear plastic, tarp, waterproof cloth, sheet of metal, plywood, pane of glass)
• Freshwater catch vessel (aluminum, plastic, wood, or stone container)
• Small rock to weight down your condensation catch surface

Steps to Follow:

1. Choose a spot that gets maximum sunlight.
2. Dig a hole using your selected digging tool.
3. Pour saltwater into the hole until it’s one-fourth full, and place your catch vessel in the center. You might need to weight it down with a small rock.
4. Cover the hole with your non-absorbent material, securing the edges with dirt or heavy objects like rocks.
5. Place a small weight, like a rock, at the center of your cover material to create a low point over the mouth of your catch vessel – this is where the evaporated water, through condensation, will start dripping into your catch vessel.

Here is a video showing a variation of this method in action:

Important Context for the Video: In the video above, the instructor advises digging a 3-foot deep hole into damp ground to extract soil moisture.

Keep in mind that if you try to dig a 3-foot hole on a sandy beach near the ocean, you will hit the water table and flood your hole with raw seawater, completely ruining your still.

For coastal survival, you need to dig a much shallower pit, line it with a tarp, or simply use a separate container of saltwater placed securely inside the hole.

Fire-Based Thermal Distillation

If you’re lucky enough to have fire-friendly weather and abundant fuel, boiling saltwater is a foolproof way to get freshwater. It’s also a lot faster than the methods recommended above.

Once you bring the water to a boil, it produces steam. As this steam cools and condenses, it transforms into droplets of water that you can collect. Here is how to do it.

Essential Items:

• Fire ignition source (lighter, match, grill starter, flint stone)
• Fire fuels (wood, brush, trash)
• Non-flammable saltwater holding vessel (large metal or tin)
• Freshwater holding vessel (metal, tin, steel, or plastic)

Process:

1. Prepare a fire in a suitable spot.
2. Position your saltwater vessel above the flames using stacked fuel.
3. Once the fire burns down to solid glowing embers, place the catch surface diagonally above the boiling water. Ensure one corner is lower than the rest to facilitate drip collection.
4. Position your freshwater vessel under the lowest corner of the catch surface so that water drips into it.

Summing It Up

Freshwater is as essential to an outdoor adventurer as a compass or a Swiss Army knife. Whether you find yourself on a sunny beach with a plastic sheet or in the woods with a fire and some stones, these methods can help you transform ocean water into lifesaving freshwater.

The amount of freshwater you collect, and the wait time, depends on your situation and adaptability.

It might seem like a daunting task to gather a gallon of water a day, but with a solid understanding of desalination and enough materials, you can maximize your freshwater collection and survive, which is the most important.

And if you’re not dealing with saline water, you can read my previous article on how to DIY a water filter for survival.

Feel free to share your own desalination stories. Every drop counts, every story matters.