The hydrodynamic drainage force of a Newtonian aqueous electrolyte solution squeezed between two surfaces of different wettability was measured using the AFM colloidal probe technique. The surface hydrophobicity, roughness, polarity and approach velocity, and thus the shearing rate of the liquid, were controlled. A direct relationship between the mobility of the aqueous electrolyte solution close to the surfaces and the hydrophobicity of the surfaces was not established. We predict that the mobility of the liquid depends in a more complex fashion on the polarity and charge of the surfaces and on the properties of the electrolyte.