The water adsorption behavior on the surfaces of chromium, copper and gold and its effect on the surface potential at various relative humidity were studied by in situ scanning Kelvin probe force microscopy (SKPFM) combined with force calibration. The thickness of water layer on different surfaces was obtained from the force-distance curve. It increases with the rise of humidity. The Volta potential map was measured using SKPFM within a wide humidity range of 20-100% as a function of the thickness of water layers. The surface potential decreases with the increasing thickness of water layers on the metal surfaces. The difference in the water adsorption behavior and its effect on surface potential originates from the different surface properties of three metals, such as the roughness and contact angle. (C) 2012 Elsevier B. V. All rights reserved.