The data set provides 3 years of almost continuous observation of water vapor in the air at 42m height on the high antarctic plateau, 123° 21' E, 75° 06' S, 3233 m above sea level. Each data is an average over the previous ½ hour. The water vapor content is measured in a heated air flow to avoid that supersaturated air at ambient temperature deposits excess moisture (above 100% with respect to ice) before reaching the humidity sensor. In fact, many reports correspond to significant supersaturation (see references provided). HMP155 thermohygrometers are used, which for the hygrometer natively report relative humidity with respect to liquid water even below 0°C. This is the variable provided in the data set, along with temperature in the heated air flow and ambient temperature. There are several conversion formulae in the literature to convert to e.g. partial pressure and relative humidity with respect to ice. As there is no clear consensus on which should be preferred in the range of temperatures at Dome C, the user is left to carry our her/his own conversions.