Oxidation is one of the most effective ways of removing organic impurities from water or recycled waste water. The kinetics and the mechanism of oxidation of two types of organic impurities were studied: soluble but recalcitrant organic impurities and the organic particles such as photo-resists, entering the recycle streams. The UV photolysis and photocatalytic oxidation of organic impurities in ultrapure water were studied in a pilot ultrapure water plant. A novel photocatalytic filter was developed by depositing a layer of photocatalytically active material on an inorganic filter substrate. A number of naturally accruing soluble and particulate organic impurities as well as surfactants were used as model impurities in this study. The photocatalyst enhanced the oxidation by both increasing the adsorption on the filter and enhancing the oxidation reaction through the catalyzed formation of active radicals.