Fragment-based drug discovery and continuous improvement of existing protein inhibitors rely on the knowledge of exactly how and how strongly a range of small molecules bind to their respective protein targets. By increasing the (perdeuterated) protein concentration, WaterLOGSY titration experiments give access to ligand binding modes even in the case of weak binders as well as to the location of protein-bound water in the surroundings of the ligand. On the basis of these findings, specific chemical modifications of the ligand could be shown to yield significantly enhanced binding affinities.