Oils and fats - of animal, vegetable or mineral origin - are the main components for a variety of products such as fuels, edible oils or fuel oils. In production processes it is quite possible that some of the oils or fats leak into the process and waste water. A large part of the costs, caused by an oil leakage and attempts to purify the contaminated water, can be saved by the use of appropriate online OIW-analyzers (oil-in-water).