Abstract: Apparatus and methods for the measurement of total organic carbon and total inorganic and organic content of water are described. A novel combination of an acidification module, and inorganic carbon removal module based on a carbon dioxide selective gas permeable membrane, and oxidation reaction system which incorporates in-situ generation of oxidizing agents, coupled with catalyzed photo-oxidation of organic compounds to form carbon dioxide; and a high sensitivity, conductometric detector employing a carbon dioxide selective gas permeable membrane permits on-line measurement of the total organic carbon content of water streams.