We have developed an interferometric optical microscope (IOM) in phase shift mode (PSM) compatible with standard liquid cells and which uses non-immersive, standard and commercially available Mirau objectives. A 15mW He-Ne laser is used for the illumination and the induced speckle pattern in canceled with a rotating diffusing glass. The interferograms displaying the interference fringes are shown in air and in water for various illumination conditions. We show a detailed comparison of the topography obtained in air and in water in HOPG with our liquid IOM (L-IOM). The noise level is very similar in air and in water and is below 1nm.