Mutual solubilities of water and the ionic liquids (ILs) 1-butyl-3-methylimidazolium hexafluorophosphate, 1-hexyl-3-methylimidazolium hexafluorophosphate, and 1-octyl-3-methylimidazolium hexafluorophosphate were measured between (278.15 and 364.15) K at atmospheric pressure. The temperature dependence of the solubilities of ILs in water and water in ILs have calculated from experimental data. The proposed correlations showed a relative maximum deviation from the experimental mole fraction data of 4.7 %. The liquid-liquid equilibrium data were correlated by the nonrandom two-liquid (NRTL) equation, and the average root-mean-square deviation of the mole fractions for the three ionic liquid + water mixtures is 0.0025.