A thin water film can easily form on the surface of an automotive radar dielectric radome during adverse weather and it causes a considerable loss of the signal power due to changes in attenuation and reflections. In this paper, influence of a thin water layer at dielectric bumper on automotive radar operating in a wide frequency interval 75-85GHz is studied. Two models are derived and analyzed to investigate water layer influence — a theoretical model that is based on the analysis of plane wave propagation in the stratified media and a numerical model that takes into account near-field propagation effects with the CST simulations. Both models are compared with the measurement results. The resulting automotive radar radome reflectances and transmittances from both models and measurements are presented as functions of the frequency and water film thickness, demonstrating possible influence of nearfield effects and measurement errors. These results can be used to estimate the influence of adverse weather conditions on the automotive radar efficiency.@en