Chemical bath deposition is a well-established process for the fabrication of thin CdS films for electro-optic devices. We investigate the various impurities in this material with emphasis on hydrogen-related compounds. Nuclear reaction analysis provides hydrogen depth profiles of chemically deposited CdS with mean concentrations up to 12 atom Fb hydrogen. Using photoelectron spectroscopy only a part of this amount can be ascribed to bonds with other impurities. The distribution of hydrogen in CdS thin films exhibits a clear dependence on the concentration of precursor substances in the bath and the deposition time. The accumulation of hydrogen in the film during processing has been determined and may be explained by a diffusion process along grain boundaries of the polycrystalline CdS. We demonstrate the variation of hydrogen and other impurity concentrations upon vacuum annealing. As a result of our investigations, we suggest a single hydrogen species is included during the deposition process in order to account for the hydrogen surplus found. A chemical reaction capable of supplying the observed individual hydrogen species is presented.