Drinking water: the problem of chlorinous odours

Chlorinous off-flavours in drinking water are a leading cause of complaints to Australian water utilities and other utilities worldwide. The occurrence and causes of chlorinous odours in drinking water were investigated with the use of an odour panel, trained using a modified flavour profile analysis technique. A new system for classifying water types according to the causes of chlorinous odours was developed in order to enable improved management strategies for the reduction of these off-flavours. Waters of ‘Type 1’ exhibit a chlorinous odour only when the free chlorine equivalent concentration is equal to or above the odour threshold concentration (OTC) for free chlorine. Waters exhibiting a chlorinous odour both above and below the OTC of free chlorine are designated ‘Type 2’. ‘Type 3’ waters are those in which the possible presence of a chlorinous odour is masked by another odour. Although causative compounds of the chlorinous off-flavours were not determined, bromine was proposed to play an important role in distribution systems where source waters have high concentrations of bromide that may not be removed by the available treatment processes. Management strategies for improvements in aesthetic water quality for each water type are proposed.