Greek symbol ${\mathrm{\psi }}_{\mathrm{w}}$ is used to denote 

Greek symbol Psi (${\mathrm{\psi }}_{\mathrm{w}}$) is used to denote water potential. ${\mathrm{\psi }}_{\mathrm{m}}$ is used to denote matric potential, ${\mathrm{\psi }}_{\mathrm{s}}$ to denote solute potential and ${\mathrm{\psi }}_{\mathrm{\rho }}$ to denote the pressure potential.