Pre-treating drinking water with ferrate(VI) before adding chlorine makes the chlorine decay faster. The faster decay can be described by two different rates. Using ferrate(VI) also reduces the formation of harmful trihalomethanes in the water. The levels of these trihalomethanes decrease as the concentration of ferrate(VI) increases. The order of trihalomethane concentrations in the water is trichloromethane > dichlorobromomethane ≈ dibromochloromethane > tribromomethane.