Can You Drink Ocean Water if You Boil It? Is it Safe?

It’s a very sensible question and one that is asked the world over. If you’re at the beach, taking a leisurely swim, and are thirsty why wouldn’t you be able to kill two birds with one stone?

However, seawater isn’t purified like the water that comes from our faucet or from a bottle at the store, and whilst it is still a natural source, it hasn’t flowed through mountainous springs for thousands of years. So, is it safe to drink?

In this article, we take a look at how safe, if at all, ocean water is to drink and if unsafe how or if it can be made drinkable.

Simply boiling ocean water will not make it safe to drink as it does not remove the salt. As the water boils it evaporates leaving the salt behind. This means boiling your seawater just makes it saltier. It will need to go through a much more rigorous scientific process to make it drinkable.

Can you Drink Sea Water?

Quite simply no, due to the high salt content in seawater it is not safe for human consumption in large amounts or as a replacement for tap, bottled, or spring water.

Ocean water is around 3.5% salt. This is due to the rocks that surround the seas. Rainwater is marginally acidic and as such, over time, erodes the rocks leaving the mineral deposits to runoff into the seas.

The human body is unable to process the amount of salt contained within the ocean waters. The more you drink the less your urine output will become, and you will eventually become dehydrated.

What Happens if I Drink Ocean Water?

Ocean water has a high salt content that the human body is unable to process. The urine that the kidneys produce will always be less salty than seawater. Consequently, you will need to have a greater output of urine than input of seawater. As this is impossible, by drinking ocean water you will eventually become dehydrated. In extreme circumstances, this can lead to death.

On average, to counterbalance 1 liter of ocean water you would need to drink 3 liters of fresh water. This itself is excessive, dangerous, and can lead to health implications.

In addition to dehydration, excessive saltwater consumption can lead to muscle cramps, high blood pressure, and sickness. Continuous ingestion of ocean water will eventually lead to organ failure and ultimately death.

Whilst we as a species can live weeks without food, should sea water be the only option when it comes to drinking, we would unlikely live longer than a few days without intensive survival knowledge of how to desalinate it.

Whilst a mouthful is unlikely to cause you any harm should it be swallowed in error, for example, whilst swimming in the ocean, in some circumstances, it can still make you sick dependent on your body and your current hydration levels.

What Happens to Sea Water if it is Boiled? Does it Remove the Salt?

Boiling seawater does not remove the salt. As the water evaporates the salt is left behind which actually leaves the remaining water saltier. This means that the water would be even more dangerous to drink.

The vapor produced when boiling salt water needs to be collected in order to provide a safe drink. There are, however, means to complete this process along with other scientific ways of removing the salt.

How Do you Make Ocean Water Drinkable?

To remove the salt the water needs to go through a process called desalination. Whilst this can be done by boiling the vapor needs to be collected, this process is known as thermal desalination.

Take a look at this short clip that explains thermal desalination.

Alternatively, a process called reverse osmosis can be used to purify saline water. This is achieved by using a semipermeable membrane to separate any contaminants from the water.

This short video explains the process of reverse osmosis and how salt minerals are filtered to produce fresh water.

How To Boil Sea Water. Making it Safe to Drink!

Simple scientific experiments can be performed at home to desalinate salt water. Thermal and solar desalination can both be accomplished using basic household objects.

Thermal Desalination at Home

You will need a lidded pan or pot with a suitable seal and a central handle on the lid. You will also need a metal or Pyrex cup in order to collect the desalinated water.

Set your pan atop the stoves and place the cup inside, in the middle. Pour the ocean water into the pan, around the cup, taking care not to spill any into the cup. Place your lid upside down and light the stove.

As the water boils and evaporates the vapor will be caught by the pan lid and drip down into the cup from the handle.

Once collected and cooled the water in the cup will be decontaminated, desalinated, and safe to drink.

Our Experiment

We carried out our very own desalination experiment. We started with a trip to the beach to collect our own ocean water. We were lucky enough to find a lovely clear rock pool so we could collect our water without having to filter the sand.

We took our seawater home and followed the instructions given above. Here are the results:

Tools required: Pan, handle with lid, heat-proof cup, seawater.
The all-important heat source. A gas flame!
We placed the heat-proof cup (which is actually a flask lid) inside the pan.
Taking care not to spill the seawater into the cup, we poured it into the pan up to approximately 1″ to make sure the cup didn’t begin to float.
We place the lid on the pan upside down making sure that the handle was directly over the cup.
Onto the heat. Time to watch and wait!
It’s working!! You can see that the vapor is being caught by the lid. The water droplets are running down the lid, onto the handle, and into the cup.
If you look carefully you can see the salt deposits that have been left behind around the pan.
YAY! We collected the water. Now we need to know if the process has worked…..

The Results

The salinity of seawater is measured using a ratio of salt in grams to water. This is written using the parts per thousand symbol ‰

Typically there are 35g of salt per 1 liter of ocean water. This reads as 35‰

We bought a specific device that measures the salinity of the water so that we could take readings both before and after our test.

A portable refractometer.

We started by taking a test reading of some shop bought bottled water we had. This, as expected read at 0‰.

It was quite difficult to take a photo of the results as you read them by looking through the machine like a telescope. However, you can still make out in the photograph below that before our experiment the reading was 35‰, and after it was 0‰.

The experiment completely desalinated the ocean water that we had collected.

Solar Desalination at Home

You will need two bowls of different sizes, Saran wrap or a sheet of thin plastic, and a small rock or pebble.

Fill your larger bowl with your salt water. Taking care not to splash any of the salt water into the smaller bowl and place it inside the larger one. Cover the top of the larger bowl with the Saran wrap making sure it is taught with no rips or holes.

Place a light rock or pebble onto the wrap over the small bowl and place your container into direct sunlight. As the water heats and the vapor rises condensation will collect on the inside of the plastic sheet. These water droplets, thanks to the pebble you placed above the smaller bowl, will then collect into the empty container.

After a few hours, your smaller bowl will have collected salt-free water which will now be safe to drink.

Whilst this method will take much longer than the stove top technique it is achievable without using additional fuel sources such as gas or electricity.

Top Tip: Place your bowls on top of black paper which will capture more sunlight and heat the water faster.