What is the losing of water from organic molecules, then the joining of these molecules.

Osmosis is a passive transport which moves water molecules from higher to lower gradient.
Osmosis then is the movement of water particles from which has water and from which has not and to provide it with the sufficient H2O. 

The concentration of salt in water affects the rate of osmosis because it will determine how much water should be transported or excreted or to be taken in. The cellular process is keen to the salt concentration of its system thus making sure to maintain balance between the salt concentration the right amount of water must also be in its area of release for any expected occurences.