Can You Freeze Salt Water? 

Last updated on October 6th, 2022 at 03:01 pm

Saltwater (whether from the ocean or used in cooking) is well known to many people. What a lot of people don’t know however is exactly whether saltwater can be frozen or not. 

If you are making a dish using saltwater you might (for whatever reason) want to save it for later. The best way to save things for a long period of time is by freezing it, but can you actually freeze saltwater? 

You can freeze saltwater although it’s harder than freezing freshwater. In fact, about fifteen percent of the ocean is frozen during parts of the year. 

Saltwater simply freezes at different temperatures than fresh water, depending on the solution of salt to water. Based on how much salt is in the water, the freezing temperature of saltwater can be anywhere from 28.4 degrees Fahrenheit, just one degree below the freezing temperature of freshwater, to -21 degrees Fahrenheit, which is the freezing temperature of salt water at a full saturate. 

When saltwater is at a full saturate, it means the water is holding as much dissolved salt as it possibly can, meaning if you put any more salt into the water, it would simply sink to the bottom water and remain separate from the water.

Water freezes when water molecules align themselves into still, symmetrical formations because the temperature forces them to stop moving. The problem with freezing saltwater is that salt also has to accomplish a similar task, but at the same time as the water. 

This is why throwing salt on ice works if the temperature is above -21 degrees Fahrenheit; the salt destroys the water’s solid state. One cool thing is that the way salt melts ice is by essentially stealing its heat, which means that when saltwater is being thawed, it’s actually colder than frozen freshwater ice.

What Happens When Saltwater Freezes? 

Saltwater will freeze just like water; it simply freezes at a lower temperature depending on the saturate of the salt/water ratio. While freshwater is well known to freeze at 32 degrees, saltwater will start freezing at around 28 degrees. 

When saltwater freezes, however, it’s only the water part of the saltwater that really freezes. You might think that this means that you can melt down frozen saltwater into drinking water. What that really means is that there’s far more freshwater on the planet than what you can find in rivers and springs; all the ice is drinkable if you melt it down. 

The problem is that it’s not that simple; salt still gets frozen in little pockets of brine in saltwater, depending mostly on how fast the saltwater was frozen. The best way to get fresh water out of it would be to thaw it and then freeze it again as slowly as possible.

Saltwater also gets denser when it gets colder. While freshwater gets its densest at 39.2 degrees, not even below freezing yet, saltwater gets denser and denser as it gets colder and colder.

Can You Get Salt Out Of Water By Freezing It? 

If you have a container of salt water and want to separate the salt from the water you might think that freezing it will allow you to do that. Afterall, I said earlier that only the water freezes so you should be able to get the salt out… right? 

You can get salt out of saltwater by freezing it but it isn’t as easy as just freezing and thawing saltwater. Saltwater will freeze at a much lower temperature than freshwater, but in the end it’s still saltwater. 

Now, the salt would slowly be expelled if you froze and thawed the water multiple times, but you would need to do it very slowly because if the freezing process happens too fast, the salt will get trapped in little pockets in the ice and simply stay there.

 On the other hand, if you are able to very slowly freeze the water, the salt will slowly be expelled from the water. A much better way to desalinate saltwater is through evaporation, where the steam from the boiling water is captured and drained in order to separate itself from the salt.

Although you can’t thaw saltwater ice to make freshwater, most glaciers and icebergs are made up of freshwater. There has been speculation as to getting freshwater by thawing icebergs by towing them inland and thawing them. 

This is probably not going to happen though.

Why Does Ice Melt Slower In Salt Water? 

The freezing and thawing of freshwater and saltwater is very interesting as it’s not exactly the same. Matter of fact, ice melts slower in saltwater than in freshwater. 

But why does this happen? 

Ice will melt slower in salt water because saltwater is denser than freshwater. This means that when the fresh water ice starts melting, it gathers around the bottom of the ice cube. 

It is then held up by the density of the salt water, and creates a little insulator layer of water causing it to melt slower. 

Can You Make Ice Last Longer By Freezing Saltwater? 

If you are planning on going on a trip across the country, you are likely to take a cooler full of ice with you. However, what happens pretty quickly is that ice in the cooler starts to melt. 

You have to keep replenishing the ice so as to keep all of your food cold. If you were to freeze saltwater instead of normal water for your cooler would the ice last longer? 

Ice made from saltwater would actually melt faster, however it would keep the cooler colder since saltwater ice freezes at a lower temperature. 

When you freeze saltwater, the salt is drawing energy, or heat, from the water around it. This has the obvious effect of melting the ice, but a strange side effect is that it actually makes the ice colder for a bit since the salt is drawing the heat into itself, making the ice colder.

So one thing that you might be able to use it for would be to use frozen saltwater in a cooler for ice. The ice would melt faster, but the temperature of the cooler would be colder.

The best way to make use of frozen saltwater for cooling things like a cooler is not to simply throw salt onto the ice you have, nor to freeze saltwater cubes. 

The best way to use frozen saltwater in a cooler is to  freeze saltwater in bottles and to put those in with the normal ice. The saltwater will thaw faster than the freshwater ice, yet it will still be colder than the ice surrounding it, meaning that you will have frozen ice for a longer period of time.

Is There A Lot Of Sea Ice?  

Up until now I’ve been talking generally about saltwater as it can be used for cooking as well as in the ocean. 

Now I want to change gears a little bit and talk specifically about frozen saltwater in the wild. 

Sea ice develops during cold seasons and melts again during warm seasons, so it differs from glaciers and ice sheets such as Antarctic ice in that way. 

About fifteen percent of the ocean water freezes during part of the year. Sea ice also forms very differently from glaciers and icebergs since it forms in the sea which is always moving while fresh water ice normally forms from snowfall. 

Sea water also has to be very cold to freeze, and since it gets denser as it gets colder, the sea around and above the ice that would form has to be far below freezing before ice can actually form. Conversely, freshwater ice such as glaciers form as a result of layer after layer of snow being overlaid and creating giant sheets of ice which break into giant icebergs.