Wastewater treatment plants, paper mills and electric power plants are major dischargers of chlorinated effluents to rivers, lakes, estuaries and the sea. At power plants chlorine is used to control fouling in cooling water while it is passing through conduits and condensers. Contact times of only a few minutes are sufficient because of the short transit time of water through a plant. The purpose of this study is to test whether dechlorination after chlorine contact times of only a few minutes can reduce or eliminate trihalomethane emissions. Trihalomethanes were determined by a gas chromatographic method.