XThe osmotic pressure arises from a compensatory effect of the tendency to reach equilibrium between a pure liquid and that same liquid in a solution. The crucial factor that prevents simple mixing is the presence of a semi-permeable membrane, which permits only the solvent molecules to flow, but not the solute molecules. While the osmostic pressure could exist in theory for any solvent this colligative property is observed in water and is ubiquitous because all life depends on membranes to protect cellular processes and those membranes are subject to osmotic forces.
