Why is it hard, and costly to remove salt from water?
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Removing the salt from saltwater is relatively easy and people have known about it and been doing it for thousands of years.
The problem is that getting fresh water the natural way from rivers and lakes and from wells and rain is so cheap that normally we don’t bother.
We have gotten so used to cheap and easily accessed water that when we see the cost for desalination it seems enormous to us.
The normal way we treat and waste fresh water becomes unsustainable when you actually have work hard and pay for it.
If you are used to getting water basically for free even the small price it costs to turn slat water into fresh water will seem enormous.
A big problem is that in order to do desalination on a big scale you first need to build a lot of machinery and pipes and stuff and that takes time.
If you wait to build these plants until it really becomes necessary and it takes years to build them, that is a problem.
Other problems include the question of what to do with all the salt.
If you just throw it back into the ocean that will destroy the marine ecosystem near your plant and slating the earth is famously what you do to your enemies not your own land.
Then there is the problem that we get slat water from the ocean and people live on land. In order to get your freshly desalted water from the ocean to where people need it you need to pump that water up and inland.
Remember that we get much of our power from the energy of rivers flowing downhill.
To pump rivers worth of water uphill to where there are droughts you would need to basically at the equivalent of reverse hydropower plants that you need to power by something.
So to do desalination on a large scale you would need to start spending huge amounts of money on new power plants and desalination plants and pipes and power lines and other stuff many years before you could actually use them and the water that you would get from it would be so expensive that we couldn’t use it like we are used to.
It is not a good solution.
Removing the salt from saltwater is relatively easy and people have known about it and been doing it for thousands of years.
The problem is that getting fresh water the natural way from rivers and lakes and from wells and rain is so cheap that normally we don’t bother.
We have gotten so used to cheap and easily accessed water that when we see the cost for desalination it seems enormous to us.
The normal way we treat and waste fresh water becomes unsustainable when you actually have work hard and pay for it.
If you are used to getting water basically for free even the small price it costs to turn slat water into fresh water will seem enormous.
A big problem is that in order to do desalination on a big scale you first need to build a lot of machinery and pipes and stuff and that takes time.
If you wait to build these plants until it really becomes necessary and it takes years to build them, that is a problem.
Other problems include the question of what to do with all the salt.
If you just throw it back into the ocean that will destroy the marine ecosystem near your plant and slating the earth is famously what you do to your enemies not your own land.
Then there is the problem that we get slat water from the ocean and people live on land. In order to get your freshly desalted water from the ocean to where people need it you need to pump that water up and inland.
Remember that we get much of our power from the energy of rivers flowing downhill.
To pump rivers worth of water uphill to where there are droughts you would need to basically at the equivalent of reverse hydropower plants that you need to power by something.
So to do desalination on a large scale you would need to start spending huge amounts of money on new power plants and desalination plants and pipes and power lines and other stuff many years before you could actually use them and the water that you would get from it would be so expensive that we couldn’t use it like we are used to.
It is not a good solution.
Mixing salt and water is an exothermic reaction, a chemical reaction which releases energy (in this case, a tiny bit of heat is released).
In chemistry, doing the reverse of an exothermic reaction is called endothermic, which means it takes energy. So, separating salt and water is necessarily endothermic, that is to say, it requires energy.
From a practical standpoint, any reaction which requires energy is going to cost more and be harder to do than on which releases energy.
Every possible method of separating salt from water requires either immense power (heat for distillation) or immense pressure (reverse osmosis). Both of these require a large amount of energy.
Almost all chemistry is like this; performing a reaction one way releases energy (exothermic) and performing it the other way takes energy (endothermic). Combining iron and oxygen to form rust produces x units of energy. Separating the rust back into iron and oxygen would take x units of energy. (And due to conservation of energy, x is the same value given the same amount of material being converted.)
Mixing salt and water is an exothermic reaction, a chemical reaction which releases energy (in this case, a tiny bit of heat is released).
In chemistry, doing the reverse of an exothermic reaction is called endothermic, which means it takes energy. So, separating salt and water is necessarily endothermic, that is to say, it requires energy.
From a practical standpoint, any reaction which requires energy is going to cost more and be harder to do than on which releases energy.
Every possible method of separating salt from water requires either immense power (heat for distillation) or immense pressure (reverse osmosis). Both of these require a large amount of energy.
Almost all chemistry is like this; performing a reaction one way releases energy (exothermic) and performing it the other way takes energy (endothermic). Combining iron and oxygen to form rust produces x units of energy. Separating the rust back into iron and oxygen would take x units of energy. (And due to conservation of energy, x is the same value given the same amount of material being converted.)
Mixing salt and water is an exothermic reaction, a chemical reaction which releases energy (in this case, a tiny bit of heat is released).
In chemistry, doing the reverse of an exothermic reaction is called endothermic, which means it takes energy. So, separating salt and water is necessarily endothermic, that is to say, it requires energy.
From a practical standpoint, any reaction which requires energy is going to cost more and be harder to do than on which releases energy.
Every possible method of separating salt from water requires either immense power (heat for distillation) or immense pressure (reverse osmosis). Both of these require a large amount of energy.
Almost all chemistry is like this; performing a reaction one way releases energy (exothermic) and performing it the other way takes energy (endothermic). Combining iron and oxygen to form rust produces x units of energy. Separating the rust back into iron and oxygen would take x units of energy. (And due to conservation of energy, x is the same value given the same amount of material being converted.)
The most straightforward way to do it is to boil the water, catch the evaporated water and condense it again to clean water. That leaves the salt residue behind as it doesn’t evaporate with the water.
The difficulty is cost. Boiling water is pretty intensive for energy. Doing it on an industrial scale would require a huge amount of energy that costs a lot.
There’s also the issue of transportation. It’s rare that an area with salt water also has no clean water: typically fresh water runs in to the sea, so if you’re beside the sea you’re almost by default also beside a fresh water supply. So you want to transport the cleaned water elsewhere. Which requires a lot of pipes and pumps. Which are expensive.
There are other ways to clean salt water. They have basically the same issues that trying to scale up & transport is still very expensive/energy intensive.
If you buy a few pipes you can easily rig up something to clean salt water yourself in your house with some pots and a stove. It’s a very simple/easy process that just happens to be expensive and therefore difficult to scale.
The most straightforward way to do it is to boil the water, catch the evaporated water and condense it again to clean water. That leaves the salt residue behind as it doesn’t evaporate with the water.
The difficulty is cost. Boiling water is pretty intensive for energy. Doing it on an industrial scale would require a huge amount of energy that costs a lot.
There’s also the issue of transportation. It’s rare that an area with salt water also has no clean water: typically fresh water runs in to the sea, so if you’re beside the sea you’re almost by default also beside a fresh water supply. So you want to transport the cleaned water elsewhere. Which requires a lot of pipes and pumps. Which are expensive.
There are other ways to clean salt water. They have basically the same issues that trying to scale up & transport is still very expensive/energy intensive.
If you buy a few pipes you can easily rig up something to clean salt water yourself in your house with some pots and a stove. It’s a very simple/easy process that just happens to be expensive and therefore difficult to scale.
The most straightforward way to do it is to boil the water, catch the evaporated water and condense it again to clean water. That leaves the salt residue behind as it doesn’t evaporate with the water.
The difficulty is cost. Boiling water is pretty intensive for energy. Doing it on an industrial scale would require a huge amount of energy that costs a lot.
There’s also the issue of transportation. It’s rare that an area with salt water also has no clean water: typically fresh water runs in to the sea, so if you’re beside the sea you’re almost by default also beside a fresh water supply. So you want to transport the cleaned water elsewhere. Which requires a lot of pipes and pumps. Which are expensive.
There are other ways to clean salt water. They have basically the same issues that trying to scale up & transport is still very expensive/energy intensive.
If you buy a few pipes you can easily rig up something to clean salt water yourself in your house with some pots and a stove. It’s a very simple/easy process that just happens to be expensive and therefore difficult to scale.
It is not that it’s hard or costly, but that we are used to water being incredibly cheap and easy to get.
It is not that it’s hard or costly, but that we are used to water being incredibly cheap and easy to get.
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