The ''water-dragging'' effect is characterized by the amount of water ''dragged'' into a water-insoluble organic solvent by a solute partitioning between water and this solvent.1 In this study, 62 structurally diverse compounds (ortho-, meta-, and para-substituted phenols, carboxylic acids, alcohols, amines, miscellaneous aprotic solutes, and diastereomeric ephedrines) were investigated. The results were analyzed by an equilibrium model and ''pressed in terms of the macroscopic stoichiometry of hydrates and an equilibrium constant of hydrate formation. The macroscopic stoichiometry of hydrates being close to one (range 0.5-1.5), a normalized equilibrium constant (log K(w)') was calculated for a stoichiometry fixed to a value of one. On this basis, the water-dragging effect was shown to be due primarily to the H-bond-donor acidity of solutes and secondarily to their H-bond-acceptor basicity. In addition, intramolecular effects (e.g., internal H-bonds) and solvent accessibility strongly modulate the water-dragging effect