The formation of water containing crystal forms, so-called hydrates, is a real problem for the pharmaceutical industry. Hydrates show thermodynamically the lowest solubility in water and thus in bodily fluids, and can thus jeopardise the efficiency and safety of a medicine. We are investigating the aggregation of drug molecules with water in solution before crystallisation in order to evaluate the hypothesis that the more stable the resulting hydrate, the stronger the interaction in solution has to be. This work is mainly carried out by lab-based solid-state analytical methods and solution spectroscopy (FTIR and NMR). However, in order to validate our results we now propose to measure neutron total scattering of these solutions to obtain structural information. The chosen model compound is diatrizoic acid, which forms a very stable dihydrate from DMSO water mixtures.