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 nor model input is described and the results are compared with other current approaches. The ability to capture sharp water structures is illustrated by comparisons with radiosonde measurements and global circulation analyses from NCEP and ECMWF. It is shown that the method described is able to detect thin layers of water, and allows retrieving atmospheric water profiles in cases where the ancillary data are not optimal.