How to Make Salt Water and Seawater Drinkable (And Why You Cannot Just Drink It)
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Quick answer: do not drink seawater. It contains more salt than your kidneys can remove, so drinking it dehydrates you. Boiling does not remove salt. To make seawater drinkable you need desalination, such as distillation (boil water and collect the condensed steam), a solar still, or a reverse osmosis desalinator. Always desalinate in a clean setup and avoid water contaminated with fuel or chemicals.
If you are stranded at the coast or on a boat, seawater looks like unlimited water, but it will make you worse off if you drink it. This guide explains why, what desalination is, practical ways to do it from a pot or a solar still, and what to avoid. It follows NOAA, USGS, CDC and Ready.gov information. It is general information, not medical advice. If you or someone else has been drinking salt water and feels very sick, get medical help.
Why you cannot drink seawater
NOAA explains that human kidneys can only make urine that is less salty than seawater. To get rid of the excess salt from seawater, your body has to urinate more water than you drank, so you end up dehydrated and thirstier, which can eventually be fatal. The USGS adds that your kidneys need fresh water to dilute the salt, and if there is too much salt in your body they cannot do that. A physiology textbook gives the math: for every liter of seawater drunk, the body loses roughly half a liter more water than it took in. This is why castaways who drink seawater get into trouble quickly.
What is desalination?
Desalination means removing salt and other dissolved minerals from water. At home or in the field that usually means distillation, which boils the water and condenses the vapor, leaving the salt behind. Large plants and some portable emergency devices use reverse osmosis, which pushes water through a very fine membrane. The CDC’s travel guidance notes that only reverse osmosis can desalinate water for ocean travel among field treatment methods, so a purpose-built desalinator is the most practical option on a boat.
Can you boil salt water to make it drinkable?
Not by itself. Boiling kills germs but leaves the salt behind, and as water evaporates the remaining water becomes saltier. A CDC document on tsunami water quality warns that boiling brackish water for a long time can increase the concentration of salts and other contaminants. Boiling is only part of distillation, where you capture and cool the steam to collect the fresh water.
Simple ways to make seawater drinkable
Stove-top distillation
Ready.gov describes a basic method: fill a pot halfway with water, tie a cup to the handle of the pot’s lid so that it hangs right-side-up when the lid is upside-down, making sure it does not dangle into the water, and boil for about 20 minutes. The water that condenses and drips from the lid into the cup is distilled. Let it cool before drinking. Ready.gov notes that distillation removes microbes plus heavy metals, salts and most other chemicals.
- Use a large pot with a lid that you can invert, and a heatproof cup.
- Keep the cup out of the seawater so it collects only condensed steam.
- Take care with hot steam and boiling water. Burns are a real risk.
- Distilled water tastes flat. Pouring it between clean containers can help, and the CDC suggests adding a pinch of salt per quart if you wish.
- Make sure all of your equipment is clean.
Solar distillation
A solar still uses the sun’s heat to evaporate water in a sealed container and collects the condensation. It needs no fuel, but it yields only small amounts, often a few cups a day under good sun, and the exact output depends on the design and weather. Treat it as a supplement rather than your only source. Inflatable solar stills sold for emergency kits follow the same principle, and we previously mentioned the Aquamate Solar Still. We have not verified current specifications, so check the manufacturer details before you buy.
Countertop and electric distillers
Home water distillers run on electricity and make distilled water from tap water or other water. They need power, so they are better for a prepared home than a field emergency. We previously mentioned the Megahome countertop distiller; check current details before relying on any model, and remember that salt water can corrode some equipment, so read the manual first.
Reverse osmosis desalinators
Manual reverse osmosis desalinators, designed for lifeboats and sailors, are the most practical field option for large amounts of seawater. They are specialized equipment, so read the instructions and practice before you need one.
Water to avoid, even after treatment
The CDC says you cannot make water containing fuel, toxic chemicals or radioactive materials safe by boiling or disinfecting. Seawater near a spill, harbor or industrial site may be contaminated, so use another source if you can. After desalinating, make sure water is also microbiologically safe, and store it in clean containers. See our guide to storing water for emergencies.
How much seawater can you drink?
NOAA says drinking seawater can be deadly, and there is no safe survival amount. Older claims that you can drink small amounts, or mix seawater with fresh water, are not supported by NOAA or USGS guidance. If you must ration, drink fresh water, minimize activity and stay shaded, and collect rain when you can. Rain should be collected cleanly and treated if there is any doubt.
What happens if you drink seawater?
- Nausea and vomiting are common because salt irritates the stomach. Vomiting causes further fluid loss.
- Increasing thirst and dehydration, because the kidneys must use more water than you drank.
- Diarrhea can add to dehydration.
- Very high blood sodium can cause confusion, weakness and in severe cases seizures and organ failure.
- Contaminated seawater can also cause infections.
This list is general information, not medical advice. Anyone who drank a significant amount of salt water and feels very ill should get medical care.
Is a saltwater flush a good idea?
No. A saltwater flush is sometimes promoted as a cleanse, but the same physiology applies: a large dose of salt water can cause vomiting, diarrhea, dehydration and dangerous sodium levels. Do not do it, and talk to a health professional if you are considering it for any reason.
Other options for water at the coast
If you are near the coast and have a way to find fresh water, rainwater, dew, a nearby stream or a well may be safer. Water from these sources can still carry germs, so treat it using the CDC methods described in our guide to purifying water from any source and boiling water without electricity.
Frequently Asked Questions
Can you drink seawater to survive?
No. NOAA and the USGS say it dehydrates you and can be deadly.
Does boiling seawater make it safe?
Boiling kills germs but leaves the salt behind, so it does not make seawater drinkable. You need to capture and condense the steam.
What is the simplest way to desalinate water?
Distillation, such as boiling in a pot with an inverted lid and a cup to collect drips, as Ready.gov describes. A reverse osmosis desalinator is best for larger amounts.
Can I mix seawater with fresh water?
Not as a survival strategy. Official guidance does not support drinking diluted seawater.
What if the water has fuel or chemicals in it?
Do not use it. The CDC says boiling or disinfecting cannot make it safe.
Bottom line
Never drink seawater. Desalinate it by distillation or reverse osmosis, avoid contaminated sources, keep your equipment clean and treat all water carefully. This article is general information, not medical advice.
