Inverse micelles of surfactant AOT at low water contents are studied. From RMN measurements the molar fraction of bound water was obtained. Ultrasonic measurements, which depend on the compressibility, permit to determine the internal radius (water radius) of the micelles. With both results, the size of the bound water layer in this system was found around 0.3 nm. Correlated changes in the FT‐IR absorption spectra give us information about the interaction between water and the polar head of AOT. Multilamellar vesicles, at different concentrations, of phospholipid DPPC, studied by DSC and FT‐IR present a sub‐zero transition near −40°C. This transition is attributed to the interstitial water, i.e. the water confined between two DPPC bilayers. These results emphasize the peculiar properties of the bound water in such systems.