GPS radio occultations provide high-resolution vertical profiles of the atmospheric refraction index that can be used to extract vertical profiles of tropospheric moisture content. A physical method to extract water abundances from refraction index profiles without using ancillary data or model input is described. The ability to capture sharp water structures in the upper troposphere is illustrated by comparisons with current approaches, individual radiosonde measurements, and statistics against global circulation analyses from the National Centers for Environmental Prediction and European Centre for Medium-Range Weather Forecasts. It is shown that thin layers of significant moisture variability can be detected and that atmospheric water profiles can be retrieved even in cases where the ancillary data are not optimal.