Group contribution methods to estimate water solubility have been studied on the basis of a test set of 694 organic nonelectrolytes, consisting of 351 liquids and 343 solids with experimental data taken from literature after critical evaluation. Derivation of a new fragmentation scheme leads to a squared correlation coefficient of 0.95 and an average absolute calculation error of 0.38 log units, which is superior to other group contribution methods currently available. Differences in performance for individual classes of compounds are discussed in detail. Solubility prediction for liquids is generally better than for solids, and the results support the inclusion of a melting point term to account for the entropy of fusion of solids.