Pure water has maximum water potential due to the following reasons:
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Water potential is the chemical potential of water. It indicates the free energy related to water.
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Water molecules possess kinetic energy in liquid as well as gaseous state which are in constant rapid motion.
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Greater the concentration of water in a system, greater the kinetic energy of its water potential.
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If we consider two systems having water (example: cell and solution), random movement of water molecules will take place from the system having higher energy to the one with lower energy. At equilibrium, water will move from the system containing water at higher potential to the one having a low potential.
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Water potential is represented by the Greek symbol Psi. It is expressed in pressure units like pascals.
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Water potential of pure water at defined temperature and pressure is taken to be zero.
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If solute molecules are dissolved in pure water, its concentration decreases, thereby, reducing its water potential.
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So, all solutions have a lower water potential than pure water.
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The magnitude of the lowering due to dissolution of solutes is termed as solute potential and is always negative.
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Higher the solute molecules, the lower or more negative the solute potential.
