Water potential : Greater the concentration of water in a system, greater is its kinetic energy or “water potential”. Hence pure water will have greater water potential . By convention, the water potential of pure water at standard temperatures, which is not under pressure is taken to be zero. Osmotic potential or Solute potential: If some solute is dissolved in pure water, the solution has fewer free water molecules ,reducing the water potential. Osmotic potential is negative when a solute is dissolved. Hence for a pure water which lacks solutes, the osmotic poptential will be zero.