Define water potential and solute potential.

(N/A) $\Rightarrow$ Water potential: Water potential is the potential energy of water per unit volume. It represents the free energy of water molecules. The water potential $(\Psi_{w})$ of pure water at atmospheric pressure is defined as zero. The unit of water potential is Pascal $(Pa)$ or Bar $(1 \text{ MPa} = 10 \text{ bars})$.
$\Rightarrow$ Solute potential: When solutes are added to pure water,the free energy of water decreases,making the water potential negative. This reduction in water potential due to the presence of solute particles is known as solute potential or $(\Psi_{s})$. It is always negative in a solution.