The objective of the paper is to use life cycle assessment to compare environmental impact of different technologies used in the process of water disinfection. Two scenarios are developed for water disinfection life cycle at ZUW Raba water treatment plant: (1) historical, in which gaseous chlorine is used as a disinfectant and (2) actual, in which UV radiation and electrolytically generated sodium hypochlorite are used for that purpose. Primary data is supplemented with ecoinvent 3 database records. Environmental impact is assessed by IMPACT2002+ method and its midpoint and endpoint indicators that are calculated with the use of SimaPro 8.4 software. The focus of the assessment is on selected life cycle phases: disinfection process itself and the water distribution process that follows. The assessment uses the data on ﬂows and emissions streams as observed in the Raba plant. As the results of primal analysis show, a change of disinfectant results in quantitative changes in THMs and free chlorine in water supplied to the water supply network. The results of analysis conﬁrm the higher potential of THMs formation and higher environmental impact of the combined method of UV/NaClO disinfection in distribution phase and in whole life cycle, mainly due to the increase of human toxicity factors. However, during the disinfection phase, gaseous chlorine use is more harmful for environment. But the ﬁnal conclusion states that water quality indicators are not signiﬁcant in the context of LCA, while both disinfection and distribution phases are concerned.