The results of the first energy-dispersive reflectivity measurements with a (membrane coated) liquid surface are reported. They rely on the calibration curve measured with pure water and can be done without any sample or detector movement with a low-intensity, laboratory-based X-ray generator within less than 1 h. As an illustration, the structural parameters of a diarachidoylphosphatidylcholine monolayer at the air/water interface are determined. It is argued that the energy-dispersive detection in combination with the intense synchrotron radiation can be used for the time-resolved reflectivity measurements on the time-scale of minutes.