How to Desalinate Seawater with Household Items

You can desalinate seawater at home using three main methods: solar distillation (using a bowl, plastic wrap, and sunlight), stovetop boiling (using a pot with an inverted lid to catch steam), or freezing (using your home freezer where ice forms with less salt than the surrounding water). The two most common distillation methods for survival in emergencies rely on evaporation to distill water, where heating saltwater forces water molecules to transform into a gaseous state and evaporate, separating the water from salt and other impurities.

These techniques won’t produce large quantities quickly, but they work when you need emergency drinking water.

Why You Can’t Just Drink Seawater

Before we get into the how-to, let’s talk about why this matters. The concentration of salt in the ocean is four times higher than the concentration of salt in the human body, and human kidneys can only make urine that is less salty than ocean water. This means your body would need to use more water than you drank just to get rid of the excess salt. You’d end up more dehydrated than when you started.

The recommended maximum salinity for drinking water is 500 mg/L (in some cases 1000 mg/L), while seawater can contain between 18 and 45 g/L of salts. That’s a massive difference.

Understanding How Desalination Works

Think about how rain forms. Water evaporates from the ocean, rises into the sky as water vapor (leaving the salt behind), and eventually falls back down as fresh rainwater. That’s nature’s desalination system, and we’re going to copy it on a smaller scale.

The science is straightforward: salt doesn’t evaporate with water. When water turns into vapor, it leaves dissolved minerals and salts behind. When that vapor cools and turns back into liquid, you get fresh water.

Method 1: The Solar Still (Bowl and Plastic Wrap)

This is your go-to method when you have no fuel or electricity. It’s slow but reliable, and it runs entirely on sunlight.

What You Need

• One large bowl or container (the bigger, the better)
• One small cup or glass
• Clear plastic wrap or a plastic sheet
• A small rock or pebble
• Seawater
• Direct sunlight for several hours

Step-by-Step Instructions

Start by filling your large bowl about halfway with seawater. Don’t fill it all the way up because you need to place a smaller container in the middle.

Carefully place the small glass in the center of the bowl, being careful not to get any salt water into the glass. This glass will catch your fresh water.

Stretch clear plastic wrap tightly over the top of the bowl and seal it around the edges, making sure it’s airtight so moisture doesn’t escape. If the plastic doesn’t cover the entire opening, use two pieces and tape them together.

Place a small rock or marble in the center of the plastic wrap, right above the jar. This creates a depression, like a funnel, so water droplets will roll down to the center and drip into your collection cup.

Set your solar still in direct sunlight. You want the sunniest spot you can find, and you’ll need to leave it there for several hours.

What Happens Inside

The heat of the sunlight gets into the bowl, and the plastic traps the warmth inside, creating a greenhouse effect that heats up the salt water and turns it to vapor. Since water evaporates at a much lower temperature than salt, the salt is left behind in the bowl.

When the water vapor hits the cooler plastic at the top, it condenses into droplets. These droplets follow the slope created by your rock and drip into the collection cup in the center.

How Much Water Can You Get?

Don’t expect miracles. A solar still isn’t the fastest method to get pure water, but it is effective. A day of sunlight might yield about one quarter cup of fresh water. If you need more, set up multiple bowls.

The amount depends on several factors: how sunny it is, how large your setup is, and how hot the day gets. Cloudy days will produce almost nothing.

Method 2: The Ground Pit Solar Still (Outdoor Version)

If you’re outside and have more space, this larger version works better for producing more water.

What You Need

• A shovel or digging tool
• Clear plastic sheeting
• A container for collecting water
• Rocks or soil to anchor the plastic
• A small rock or weight
• Optional: a drinking tube

Building Your Still

Dig a pit that is about 4 feet wide and 3 feet deep, then dig another small hole in the center of the pit and place the water container there. If you have a plastic tube, run it from the container to the outside edge so you can drink without opening the still.

Pour seawater into the pit around your collection container, or let the ground moisture do the work. If you have vegetation like leaves or grass, add them to the pit. This adds more moisture to help the process.

Cover the pit loosely with a plastic sheet and use stones or other heavy objects to hold it in place over the pit, making sure that the lowest part of the plastic sheet hovers directly over the bowl. Place a small rock in the center of the plastic, directly above your collection container, to create a downward slope.

The plastic needs to be sealed around the edges with soil so no moisture escapes, but it shouldn’t touch the bottom of the pit or your collection container.

This type of solar still without vegetation can produce anywhere from a few hundred milliliters to 1 liter of water in 24 hours, depending on the weather, the soil’s moisture, and the still’s size.

Method 3: Stovetop Distillation (The Fastest Household Method)

This method uses heat from your stove to speed up the evaporation process. It’s much faster than solar methods but requires fuel.

What You Need

• One large pot with a lid
• One small heat-safe cup or bowl
• A stove or campfire
• Seawater
• Ice cubes or cold water (optional, but helpful)

How to Do It

Fill your large pot with seawater, but only about halfway. You need room for the smaller container.

Place the lid on the large pot upside down, which will allow the steam to condense on the lid and drip into the smaller container. The lid needs to be inverted so the condensed water drips back down to the center instead of running to the edges.

Set your small heat-safe container (a ceramic mug or metal bowl works great) in the center of the pot. Make sure no seawater splashes into it. This will catch the fresh water as it drips from the lid.

Place the large pot on a heat source, such as a stove or campfire, and bring the water to a boil.

As the water boils, steam will rise and condense on the underside of the lid, and the condensed water droplets will then drip into the smaller container.

Here’s a trick to speed things up: place ice or cold water on top of the inverted lid to speed up the condensation process by cooling the steam more quickly. The bigger the temperature difference, the faster condensation happens.

Keep an eye on the process. Make sure the water keeps boiling and check periodically to see how much fresh water has collected in your container.

Important Safety Notes

The pot and lid will be extremely hot. Use oven mitts or thick towels when checking your progress. Don’t pour out the seawater until everything has cooled down, or you might accidentally dump your fresh water collection.

Steam can cause serious burns. Keep your face and hands away from the steam, and be extra careful when removing the lid.

Method 4: Freezing Desalination (Yes, You Can Use Your Freezer)

This method sounds counterintuitive, but it works because ice forms with less salt than the surrounding water.

The Science Behind It

Freeze desalination is based on salt rejection from water during freezing, where the small dimensions of the ice crystal lattice exclude salt ions during partial freezing instead of being incorporated in the crystal lattice of the ice.

When saltwater freezes, pure water molecules form ice crystals first, while the salt gets pushed out into the remaining liquid. This is why ocean ice is less salty than ocean water.

How to Try It at Home

Fill a plastic container with seawater and place it in your freezer. Don’t fill it completely because water expands when it freezes.

A removal of nearly 48% to 62% of salt can be achieved with a total water recovery of 85 to 90%. The key is to freeze the water partially, not completely.

Let the container freeze until you have a good layer of ice forming around the edges and top, but the center is still liquid. This might take a few hours depending on your freezer temperature.

Remove the container from the freezer. The ice on the outside and top is your freshwater (well, fresher water). The concentrated brine in the center needs to be discarded.

Carefully separate the ice from the remaining liquid. You can drain the liquid brine, or carefully scoop out the ice. Let the ice melt, and you have water with significantly less salt.

The Reality Check

Until now, freeze desalination method has not been applied in commercial scale and studies are limited to laboratories and small pilot plants due to the incurred capital cost and complex operation of ice separation and melting processes. For home use, it’s more of a curiosity than a practical solution, but it can work in a pinch, especially in cold climates where you can use natural freezing instead of a powered freezer.

What to Know Before You Start

These Methods Are Slow

All of these household methods produce water slowly. Commercial desalination plants process millions of gallons per day. Your bowl on the counter? Maybe a cup if you’re lucky. This is emergency water, not a replacement for your tap.

The Water Won’t Be Perfect, But It’s Safe

Distillation removes salt, but distilled water lacks essential minerals such as calcium, magnesium, and potassium, which are important for maintaining overall health. For short-term emergencies, this is fine. For longer-term use, you’d need to add minerals back or eat a varied diet to compensate.

The good news? Distillation removes virtually everything from water, including bacteria, viruses, heavy metals, and other contaminants. It’s one of the most thorough purification methods available.

Your Collection Containers Matter

Whatever container catches your fresh water needs to be clean. Really clean. You’re going through all this work to purify water, so don’t contaminate it with a dirty cup. Sterilize your collection containers with boiling water before you start.

Energy and Fuel Considerations

The latent heat of freezing and vaporization of water is 330 kJ/kg and 2256 kJ/kg, respectively, meaning the freeze desalination process needs approximately 1/7th of the energy required by the vaporization-based desalination processes. In practical terms, boiling water uses a lot of fuel. If you’re in a survival situation, solar methods are more sustainable even though they’re slower.

The Scale Problem: Why This Isn’t a Long-Term Solution

As of 2019, there were 15,906 desalination plants operating globally, producing 95 million m³ of freshwater per day, with 48% of desalinated water produced in North Africa and the Middle East. These industrial plants use sophisticated technology like reverse osmosis and multi-stage flash distillation.

They’re designed for scale and efficiency in ways that household methods simply cannot match. Your bowl-and-plastic-wrap setup is brilliant for emergencies, but it’s not going to supply enough water for regular daily needs.

When These Methods Make Sense

Understanding when to use these techniques is as important as knowing how to do them.

Emergency Situations

You’re stranded near the coast after a natural disaster. Your municipal water supply is contaminated. You’re on a boat and your fresh water supply has run out. These are the scenarios where knowing how to desalinate seawater with household items becomes invaluable.

The human body can only survive about three days without water, and symptoms of dehydration such as fatigue, confusion, and organ failure can occur long before that. Having this knowledge could literally save your life.

Educational Projects

Want to teach kids about the water cycle, evaporation, and condensation? These methods are perfect hands-on science experiments. They demonstrate real-world applications of basic scientific principles.

Off-Grid Living Supplements

If you live off-grid near the coast, these methods can supplement other water sources. They won’t be your primary source, but they can contribute to your overall water security strategy.

Common Mistakes to Avoid

Don’t Drink the Seawater While You Wait

It’s tempting when you’re thirsty, but to get rid of all the excess salt taken in by drinking ocean water, the person would have to urinate more water than they drank, and eventually, the person would die of dehydration. Stay strong. Wait for your desalination process to work.

Don’t Let the Plastic Touch Your Collection Container

If the plastic wrap or sheet touches your collection cup in a solar still, condensation won’t drip into it properly. The whole system depends on that gap and the slope created by your weight in the center.

Don’t Forget to Seal Your Solar Still

If you don’t have the edges of your plastic sealed, steam can escape out the sides meaning you will be losing water that you could have been collecting. Every bit of escaping moisture is water you won’t be drinking later.

Don’t Rush the Freezing Method

Freezing all the water completely doesn’t help. You need that separation between the fresher ice and the saltier liquid center. Partial freezing is the key.

Improving Your Results

Use Multiple Stills

Even in ideal conditions, it takes a long time to collect any significant amount of water, so if you have plenty of materials, time, and opportunity you should definitely consider setting up multiple solar stills to increase the net yield of potable water from them.

Increase Surface Area

The more surface area your seawater has, the faster evaporation happens. A wide, shallow container works better than a narrow, deep one for solar stills.

Pre-Filter When Possible

If your seawater is cloudy or full of debris, try to filter it through cloth or sand first. Cleaner water evaporates more efficiently and produces cleaner distilled water.

Use Reflectors

Some people have success adding aluminum foil or reflective material around their solar still to direct more sunlight and heat into the system. It’s not necessary, but it can increase output.

The Professional Perspective

While we’re focusing on household methods, it’s worth understanding what the professionals use. In reverse osmosis, water molecules are separated from seawater using high-tech and expensive technology where saltwater is forced through thousands of semipermeable membranes under extreme pressure.

These membranes allow smaller water molecules to pass through while blocking larger salt molecules. It’s remarkably efficient but requires specialized equipment and lots of pressure.

For coastal communities, small islands, and ships at sea, reverse osmosis devices have become the standard. They’re expensive, but they produce clean water much faster than any DIY method.

Regional Considerations Around the World

Different parts of the world face different water challenges. In the Middle East and North Africa, where freshwater is scarce, desalination provides a lifeline for millions of people. In island nations, it ensures water security regardless of rainfall patterns.

Understanding these global contexts helps us appreciate why desalination technology continues to advance and why knowing the basics might become more important as climate patterns change and freshwater becomes scarcer in more regions.

Health and Safety Considerations

Is Desalinated Water Safe to Drink?

Yes, properly desalinated water is safe to drink. The resulting water exceeded World Health Organization quality guidelines in tests of portable desalination devices.

The main consideration is that pure distilled water lacks minerals. Desalting processes significantly reduce virtually all ions in drinking water to the point where people who traditionally consume unreconstituted desalted water may be consistently receiving smaller amounts of some important nutrients.

For emergency use over a few days or weeks, this isn’t a problem. Your body has reserves, and the minerals in the food you eat will compensate. For longer-term consumption, you’d want to either blend your desalinated water with mineral-rich water or add minerals back through supplements or a varied diet.

What About Boron and Other Contaminants?

The most important contaminant is probably boron, which might exist at high concentration in seawater and might not be removed completely by reverse osmosis plants. Household distillation methods, which involve boiling or evaporation, effectively remove boron since it doesn’t evaporate with water.

Children and Desalinated Water

Children are particularly vulnerable to health risks from ingestion of demineralized water and can readily over-hydrate their optimal needs by continuing to drink water. If you’re using desalinated water for children in an emergency, make sure they’re also eating food that provides minerals, and don’t let them drink excessive amounts.

Building a Complete Water Security Strategy

Desalinating seawater with household items is one tool in your emergency preparedness kit, but it shouldn’t be your only tool. Store fresh water in food-grade containers. Have water purification tablets or filters on hand. Know where natural freshwater sources are in your area. Learn multiple methods for obtaining and purifying water.

Think of desalination as your backup plan for the backup plan. It’s there when everything else has failed and you’re near a source of saltwater.

The Future of Household Desalination

Technology continues to advance. Researchers have developed portable desalination devices that work with the push of a button. The user-friendly unit, which weighs less than 10 kilograms and does not require filters, can be powered by a small, portable solar panel.

These devices might eventually become as common in emergency kits as flashlights and first aid supplies. But until that day comes, knowing how to make your own desalination system with items from around your house remains a valuable skill.

Final Thoughts

You won’t be opening a water bottling company with a bowl and some plastic wrap. You won’t even produce enough water to take a proper shower. But you will have access to drinkable water when you need it most, and that’s worth everything.

These methods work. They’re based on solid scientific principles that humans have understood and used for thousands of years. The ancient Greeks knew that seawater turned into freshwater when evaporated and condensed. You’re just applying that same knowledge with modern materials.

Practice these methods before you need them. Try making a solar still on a sunny weekend. Experiment with the stovetop method. See how much water you actually get and how long it takes. That hands-on experience will be invaluable if you ever face a real emergency.

The ocean covers most of our planet. Knowing how to safely extract freshwater from it, even on a small scale, gives you a powerful tool for survival. Whether you’re preparing for natural disasters, planning off-grid adventures, or simply curious about the science, these household desalination methods are practical skills worth knowing.

Stay safe, stay prepared, and remember that knowledge is one resource that never runs out.