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In order to turn sea water into drinkable water, virtually all of the salt must be removed. By definition, salts are ionic compounds. I am assuming that there are other non-ionic compounds devolved in the sea water, must these compounds be removes as well before water becomes safe to drink? In general, do non-ionic compounds present the same dehydration dangers as salts when consumed in drinking water? Why or why not?

For this question, lets not consider other toxic effects besides dehydration.

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    $\begingroup$ Whether the solute is ionic or not actually has little to do with the danger of drinking sea water. The amount of solute is the problem. If the oceans were made of syrup (a non-ionic sucrose solution in water) with the same molar concentration as salt in seawater, then I think they would be just as deadly, by about the same mechanism as seawater; solutions more concentrated than blood pull water out of cells by osmosis, killing them from dehydration. $\endgroup$ – Nicolau Saker Neto Jul 30 '14 at 2:30
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    $\begingroup$ It's not as simple as that. If the ocean were made of syrup (0.6M glucose instead of 0.6M ionic salts) it would be food. You could live on it, together with some protein and other nutrients. Consider also that many creatures live in the sea, and they don't lose all water. $\endgroup$ – Silvio Levy Jul 30 '14 at 17:09
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Actually, the salt in seawater doesn't kill you directly. It dehydrates you and you die of thirst. If you mixed 1 part of seawater with 2 parts of fresh water, it would not dehydrate you, but you would need to eliminate the excess salt so you would need to drink a lot of this salty water.

There are many living things in seawater that can kill you. Red Tide (excuse me, harmful algal bloom) is an algae common to warm water that produces a toxin. Very little of this toxin is needed to kill a person.

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Yes, non-ionic but solvable compounds, if present in high enough concentration in water, can dehydrate human. For example, sugars, if present in high concentrations, dehydrate living organisms, and this is the reason why honey can be stored for years without significant loss in quality. Sugar sirup is a well known preservative, traditionally used in slavic countries to preserve fruits and berries.

However, seawater contains very little amount of non-ionic compounds, and most of them belongs to living things of various nature and, to some extent, their wastes. Moreover, traditions schemes of desalination filters off this impurities as well. This is actually a problem, as perfectly clean water is not healthy to consume, so generally it is preferable to add some carefully balanced amount of salts to such water.

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  • $\begingroup$ If all of the ionic substances are removed, would salt water still contain a toxic level of dissolved substances? $\endgroup$ – Hoytman Jul 31 '14 at 19:30
  • $\begingroup$ @Hoytman To my knowledge, no. $\endgroup$ – permeakra Jul 31 '14 at 19:32
  • $\begingroup$ @Hoytman To be precise, some volumes of seawater may contains toxic compounds on their own, but these are special cases. For example, deep waters of Black Sea contains (mostly not dissociated) hydrogen sulfide. $\endgroup$ – permeakra Jul 31 '14 at 19:34

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