The influence of the amphiphile 1,3-dimethylurea (1,3-DMU) on the dynamic properties of water was studied using dielec. relaxation spectroscopy. The expt. provided evidence for substantial retardation of water reorientation in the hydration shell of 1,3-DMU, leading to a sep. slow-water relaxation in addn. to contributions from bulk-like and fast water as well as from the solute. From the amplitudes of the resolved water modes effective hydration nos. were calcd., showing that each 1,3-DMU mol. effectively freezes the reorientation of 1-2 water mols. Addnl., a significant amt. of solvent mols., decreasing from ~39 at infinite diln. to ~3 close to the soly. limit, is retarded by a factor of ~1.4 to 2.3, depending on concn. The marked increase of the solute amplitude indicates pronounced parallel dipole alignment between 1,3-DMU and its strongly bound H2O mols. Mol. dynamics (MD) simulations of selected solns. revealed a notable slowdown of water rotation for those solvent mols. surrounding the Me groups of 1,3-DMU and strong binding of ~2H2O by the hydrophilic carbonyl group, corroborating thus the exptl. results. Addnl., the simulations revealed 1,3-DMU self-aggregates of substantial lifetime.