Abstract: A device and a method for detecting deposits on surfaces includes a body having a surface on which deposits occur and influence reflection properties of the surface to electromagnetic radiation. A transmitter transmits electromagnetic radiation to the body and a detector detects the presence of the deposits at the surface. The detector measures electromagnetic radiation received from the transmitter after reflection at the surface. Preferably, the device and method are used in a liquid-conveying machine, particularly, a washing machine and/or a dishwasher. Particularly, light is introduced into the light-guiding body to detect the presence of the deposits. The light is internally reflected by the surface and is guided to a sensor. If deposits occur on the surface, the deposits affect the light-reflecting properties of the surface, and the affect is detected by the sensor.