Can you not boil salt water to make fresh water?

Question

I always hear people trying "better" ways of converting salt water to fresh, but wouldn't boiling it and capturing the steam be an effective and viable way of doing thison a large scale? I know that the salt stays in the water when it evaporates, this is why the dead sea is so salty.I never really researched it, but to me, this would be by far the cheapest, easiest way to do it. Am I missing something?

Answer 1

In short, yes. This is definately not the easiest way to perform the operation. Consider trying to build (essentially) a giant distillation apparatus and then trying to heat the giant flask and then having to clean the flask out. It would be a major undertaking. The most efficient way, so far, involves using membranes and the phenomena of osmotic pressure.

Basically, the water is either forced through a semi-permeable membrane (one that allows the flow of smaller solvent molecules, but not the larger solvents), known as reverse osmosis, or directing the flow of the fresh water through the membrane, by use of concentration gradients (forward osmosis).

There is alot of material to be gleaned from this website:

http://en.wikipedia.org/wiki/Desalinization

Answer 2

You don't have to boil water to evaporate it. Large scale solar stills have been tried with some success. One site listed below says that on a good day a still will produce one gallon per 8 square feet of still. At this rate an acre of solar stills might produce a little over 5000 gallons if the weather was right. A square mile might get you 3 million gallons per day. Such a plant would require maintenance. Sea water would have to be pumped from the ocean to the still and from there to the users. You would want to send the saltier water back to the ocean before it got to concentrated so you system doesn't get crusted up with solid salt. The ideal location would be a place with clear skies year round. I don't know if the US has such an area.

Answer 3

The average person uses something like 5 gallons of water a day.
For the average family of 4, that's 20 gallons a day.
To supply water for that family for a year, you would have to boil over 7000 gallons of water. Logistically speaking, the cost of generating enough heat to boil that much water would be enormous.

There is a lot of research going on to try to figure out how to desalinate water. The person that figures out a cheap and efficient way to do so will be a very rich man.

Answer 4

It's very inefficient; it requires a large amount of energy to boil water, but until recently it was the only way to make fresh water at sea. A more energy efficient process is reverse osmosis. You suck the sea water through a semi-permeable membrane and the salt is left behind.