Why is it hard, and costly to remove salt from water?
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The main problem is that salt mixes with water. If you put sand in water you can simply wait for the sand to fall to the bottom of the vessel and then simply scoop up the water (without shaking the vessel).
Why is salt more special? Well, it’s mainly because it is “soluble” in water. What this means is that a water molecule and a salt molecule stick together, as if they are holding hands. Imagine how harder it is to separate two persons holding hands (water and salt) to separating two persons simply standing next to each other (water and sand).
It’s not hard, it’s conceptually quite simple. Take salt water, boil it, condense the vapor. Any elementary school student who learns about the water cycle can understand it.
It’s *costly* because you need to heat water to its boiling point, and it takes a lot of energy to do that. That is just a physical property of water, or any substance, called its specific heat; in water’s case, you need 4184 joules of energy to make 1 kg of water 1 degree C hotter. The cost of doing so is dependent on the market price of energy, usually it works out that finding new sources of freshwater is cheaper than trying to desalinate seawater.
Reverse osmosis is another method which basically involves “filtering out” the salt from the water (to put it in five-year-old terms). It’s usually cheaper than boiling water to desalinate it, but still expensive.
The main problem is that salt mixes with water. If you put sand in water you can simply wait for the sand to fall to the bottom of the vessel and then simply scoop up the water (without shaking the vessel).
Why is salt more special? Well, it’s mainly because it is “soluble” in water. What this means is that a water molecule and a salt molecule stick together, as if they are holding hands. Imagine how harder it is to separate two persons holding hands (water and salt) to separating two persons simply standing next to each other (water and sand).
It’s not hard, it’s conceptually quite simple. Take salt water, boil it, condense the vapor. Any elementary school student who learns about the water cycle can understand it.
It’s *costly* because you need to heat water to its boiling point, and it takes a lot of energy to do that. That is just a physical property of water, or any substance, called its specific heat; in water’s case, you need 4184 joules of energy to make 1 kg of water 1 degree C hotter. The cost of doing so is dependent on the market price of energy, usually it works out that finding new sources of freshwater is cheaper than trying to desalinate seawater.
Reverse osmosis is another method which basically involves “filtering out” the salt from the water (to put it in five-year-old terms). It’s usually cheaper than boiling water to desalinate it, but still expensive.
The main problem is that salt mixes with water. If you put sand in water you can simply wait for the sand to fall to the bottom of the vessel and then simply scoop up the water (without shaking the vessel).
Why is salt more special? Well, it’s mainly because it is “soluble” in water. What this means is that a water molecule and a salt molecule stick together, as if they are holding hands. Imagine how harder it is to separate two persons holding hands (water and salt) to separating two persons simply standing next to each other (water and sand).
It’s not hard, it’s conceptually quite simple. Take salt water, boil it, condense the vapor. Any elementary school student who learns about the water cycle can understand it.
It’s *costly* because you need to heat water to its boiling point, and it takes a lot of energy to do that. That is just a physical property of water, or any substance, called its specific heat; in water’s case, you need 4184 joules of energy to make 1 kg of water 1 degree C hotter. The cost of doing so is dependent on the market price of energy, usually it works out that finding new sources of freshwater is cheaper than trying to desalinate seawater.
Reverse osmosis is another method which basically involves “filtering out” the salt from the water (to put it in five-year-old terms). It’s usually cheaper than boiling water to desalinate it, but still expensive.
It isn’t, on a small scale. It is in fact extremely easy and cheap.
The problem is *just how much water we use*. Farming and manufacturing slurp up water like the id no tomorrow. Irrigated farms use something like 42 inches of water a year. In California, that comes out to about 11 *billion* gallons of water, just for their farms.
It costs very roughly 2.4 kwh to desalinate water at home. That’s $.50 or so depending on your region. Around six billion dollars spent just on desalinating the water for farming.
It isn’t, on a small scale. It is in fact extremely easy and cheap.
The problem is *just how much water we use*. Farming and manufacturing slurp up water like the id no tomorrow. Irrigated farms use something like 42 inches of water a year. In California, that comes out to about 11 *billion* gallons of water, just for their farms.
It costs very roughly 2.4 kwh to desalinate water at home. That’s $.50 or so depending on your region. Around six billion dollars spent just on desalinating the water for farming.
It isn’t, on a small scale. It is in fact extremely easy and cheap.
The problem is *just how much water we use*. Farming and manufacturing slurp up water like the id no tomorrow. Irrigated farms use something like 42 inches of water a year. In California, that comes out to about 11 *billion* gallons of water, just for their farms.
It costs very roughly 2.4 kwh to desalinate water at home. That’s $.50 or so depending on your region. Around six billion dollars spent just on desalinating the water for farming.
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.
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