A method and apparatus for detecting the presence of water on a surface of an object using infrared radiation. A surface area to be detected is illuminated with infrared radiation having a wavelength substantially absorbed by water. An optical system is employed to view images reflected from the surface area. An optical bandpass filter is disposed between the surface area and the sensor to limit transmission of infrared light to within a specific range of wavelengths known to be strongly absorbed by water. The sensor assembly produces a signal representative of the intensity of the reflected light. If the intensity signal is lower than a predetermined level water is detected and the signal may be used to trigger alarms, record the event or otherwise control the environment of the object. The present invention is particularly suited for detecting the presence of water on a moving sheet of metal during a manufacturing process.