Solar applications of photochemical waste water oxidation methods driven by UV and/or visible light, especially TiO2/UV and the Photo-Fenton reaction (Fe2+/H2O2/UV-VIS), have been investigated. Degradation results of 4-Chlorophenol and some other model compounds at laboratory scale are discussed. A photoreactor with immobilized TiO2 has led to a higher quantum efficiency than the suspension treatment. Electron densities were calculated to predict the oxidizing properties of UV irradiated TiO2, Al doped TiO2 powders showed better performance than undoped samples in laboratory scale degradation experiments. Experiments with different waste waters (e.g. landfill leachates, plastics industry, etc.) using the Fe2+/H2O2/UV-VIS system in a photoreactor prototype are reported. Solar treatment of a model waste water in a glass basin has been investigated. Furthermore, experiments performed at the Plataforma Solar de Almeria (Spain) with different methods, reactor types and waste waters are compared. According to a comparison of costing the solar driven Fenton reaction is a cheap method for water treatment, also for highly contaminated effluents.