In industrialized countries the annual consumption of pharmaceuticals, both in the area of human medicine and in veterninary medicine, has to be classified as very high. After the application of medications in humans and in animals with the following excretion, and because of improper disposal, some stabile pharmaceuticals can enter the aquatic environment by up to ninety percent of their initial active structure. Treatment in municipal water treatment plants with their conventional process methods do not lead to a complete decomposition of these substances. There is a must for improved procedures and combinations of methods for optimal water treatment with enhanced decomposition of such pharmaceuticals. The ozonation of waste water carries a very promising potential to reach that aim. In the course of this paper in hand the oxidant ozone is analysed regarding to its properties, its possible applications and its way of production. In addition, the impact of ozone on such pollutants in water and the possible appearing reaction mechanisms have been examined closer. With the goal of developing a waste water treatment process by ozonation, that ensures a preferably complete degradation of pharmaceuticals, endocrinal substances and diverse industrial chemicals in municipal water treatment plants, laboratory experiments for the design of suitable injection systems for ozone in water and the development of contacting techniques have been carried out. The generation of ozone has been realized by using the method of corona-discharge. After the investigation of significant system components and operating parameters leading to an efficient degeneration of defined tracer substances, a semi-technical treatment plant for real municipial waste waters was constructed at the area of a nearby municipal waste water treatment plant. Based on different experiments during a few months, it was possible to evaluate the versatility and the suitability of the constructed tech scale unit that was used for further investigation of the ozone treatment procedure.