The tracer diffusion coefficient, D-w, for water (as HTO) in 28 organic solvents, including 13 esters, benzene, and 7 substituted benzenes, has been determined at 298.15 K using the diaphragm cell technique. The variation of the water diffusion coefficient with solvent viscosity (eta) is significantly different for the hydrophobic solvents (benzene and substituted benzenes, cyclohexane, hexane, and tetrachloromethane) in comparison with the other solvents, in that the D-w eta product is significantly larger (average value 3.68 x 10(-12) N compared to 1.60 x 10(-12) N). The apparent hydrodynamic radius derived from the Stokes-Einstein equation is about half the molecular radius for water diffusing in the hydrophobic solvents, and 1-1.5 times the molecular radius for diffusion in the other solvents.