The results of a neutron diffraction experiment performed on aqueous solutions of KSCN are analyzed and discussed in comparison with similar data for KCl and KOH solutions. The effect of the different ions on the structure of water and the differences and similarities among the ion solvation shells am discussed in detail. In particular it is shown that the effect of KSCN on the structure of water is visible as a shift and a broadening of the second peak of the oxygen-oxygen radial distribution function, which corresponds to a lower number of interstitial water molecules, compared to pure water. The hydration shell of the cation is similar to that found in the case of KCl solutions, and more interestingly the hydration shell of SCN- is asymmetric, with water molecules H-bonded to the N site and weakly correlated to the S site. These results provide a reasonable microscopic description of the mechanism for the high efficiency of thiocyanate in crystallizing basic proteins.