Water dynamics are investigated in binary osmolyte-water mixtures, exhibiting a microscopic heterogeneity driven by molecular aggregation, on the basis of molecular dynamics (MD) simulation studies. The protecting osmolyte TMAO molecules in solution are evenly dispersed without the formation of noticeable osmolyte aggregates, while the denaturant TMU molecules aggregate readily, generating microscopic heterogeneity in the spatial distribution of component molecules in TMU-water mixtures. A combined study of MD simulation with graph theoretical analysis and spatial inhomogeneity measurement with