Many drinking water utilities have recently changed or are seriously considering changing from disinfection with chlorine to some alternative disinfectant as a result of regulations to control trihalomethanes. Many of the water utilities that have changed to alternative disinfectants have done so without evaluating possible chemical impacts or health effects associated with the alternative disinfectant. Therefore, a research project was initiated at Jefferson Parish, Louisiana to evaluate these effects. Ozone was one of the alternative disinfectants evaluated. During the one year research study at Jefferson Parish, raw river water from the Mississippi River was pumped to the full-scale plant where it was clarified with diallyldimethyl ammonium chloride or dimethylamine-type cationic polymers. After fluoridation, but before disinfection, a portion of the clarified water was filtered through pressure sand filters before going to a 10 gallon-per-minute pilot plant.