Factors influencing formation of trihalomethanes in drinking water with special reference to Swedish conditions

The trihalomethane (THM) concentrations in drinking water are greatly affected by the disinfection methods as well as the organic content of the water. The THM formation was shown to increase considerable during 24 hours. This indicates a higher concentration of THM at the consumers' tap compared to the levels in the outgoing water from the water work. The dosage ratio between chlorine and ammonium sulphate can be used to regulate the THM concentrations. Disinfection with a relatively high dosage of chlorine dramatically increase the THM level while the equal amount of chlorine dioxide produces trace concentrations of THM only. The relatively low THM concentrations in Swedish drinking water as compared to levels found in water from for example the USA may probably depend on the low chlorine dosage practiced in Sweden.