Assessing spatial variations of water quality in the water-pipe network by analysis of THM formation

When tap water is transported over a long distance, the supplier will have to face the problem of its bacteriological safety. This necessitates a careful choice of the disinfection method in order to provide the user with water of the quality desired. The use of chlorine compounds for water disinfection favours the formation of organic halo-complexes, including trihalomethanes (THM). The increase in the THM content during transport in the water-pipe network is attributable not only to the need of applying high chlorine doses for the purpose of disinfection but also to the long time of water residence in the supply system. The paper presents an analysis of the process of THM formation in the water-pipe network of the city of Cracow. Making use of the results obtained, a model was constructed for the assessment of water recontamination due to the THM being formed, taking into account the service conditions of the water supply system. In the analysis, consideration was given not only to the operating conditions of the treatment train but also to the unstable conditions that characterize the functioning of the water-pipe network.