Are non-ionic compounds generally as dehydrating as ionic compounds in drinking water? 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.
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.