The corrosion products layer formed in natural salt waters has been characterized by impedance spectroscopy. The possibility of using synthetic waters instead of natural waters to simulate the corrosion processes has been considered. Following the EHD impedance results, it could be assumed that the mass transport of oxygen occurs in the electrolyte and through a porous layer. The AC diagrams could be described by two loops; the high frequency one is characteristic of a porous layer, whereas the low frequency one is representative of the diffusion process in the electrolyte and through the porous layer. The thickness of the corrosion products layer and the diffusion coefficient in this layer were determined by a fitting procedure. A comparison of all these parameters was given for natural and synthetic waters.