Define water potential and solute potential.

Water potential is a measure of free energy associated with water per unit volume (JM73) The water potential of pure water (Wy) at atmospheric pressure is zero. The unit of water potential is bars or Pascal (1 mPa =10 bars).
Solute Potential The addition of solutes reduce water potential (to a negative value). This reducesthe concentration of water. Hence,solutions have a lower water potential than pure water, the magnitudeofthis lowering due to dissolution of a solute is called solute potential Or ψs.