Under ambient conditions water is adsorbed on the surface of NaCl(100). We are able to explore the properties of this adlayer at 25 degrees C using infrared spectroscopic photometry and to provide its adsorption isotherm. Below 6 mbar, submonolayer water at a coverage near 0.1 is not hydrogen bonded and behaves as a two-dimensional lattice gas. In the range 8 to 16 mbar, coverages change from 0.2 to 2 water layers. This adsorbed water can be reversibly removed by lowering the vapor pressure. The diffuseness of the absorbance is consistent with a hydrogen-bonded network, and its bandcenter, near that of liquid water, suggests that the adlayer is also a liquid. A qualitative model for water adlayer growth on NaCl(100) is proposed.