The device is used for monitoring oil traces in raw, surface, process and waste water. Due to the non-contact free-fall measurement, there is no falsification of measured values as a result of window contamination and there is only minimal maintenance. The OilGuard 2 W is factory calibrated to 16 EPA-PAH standard. A secondary standard (solid reference) is available for recalibration during operation. An exact recalibration without 16 EPA-PAH is therefore possible. A sophisticated instrument design, in combination with the use of high quality optical components, minimizes the influence of interferences. As a result, the smallest as well as larger quantities of oil traces can be precisely detected. For individual adaptation, the device can be adjusted to a wide range of oils. A check with corresponding solutions is easily possible.