How to Remove Trihalomethanes from Drinking Water

During the past year, there's been much concern about trihalomethanes (THMs) in drinking water; for they are suspected carcinogens. These chemicals are formed in the drinking water treatment plant itself as a result of adding chlorine to the water. The chlorine reacts with certain organics (precursors) present in the raw water. The main factor influencing THM formation is the raw water, especially its level of precursors. Precursors can be reduced by adding an oxidant such as ozone. The amount of chlorine added also affects the production of THMs. And so doesn't the water's pH. Among means for reducing THMs: use of disinfectants other than chlorine (e.g. chlorine dioxide, ozone, and chloramine); changing the points where chlorine is added in the water-treatment process; using chlorine and another disinfectant; removing precursors; and removing THMs after their formation. Several California utilities are making progress in lowering THM levels.