Distribution of Aluminium in the Water Supply System of Sofia City, Bulgaria

Elevated concentrations of aluminium have been found at the outlets of the Drinking Water Treatment Plants (DWTPs) of Sofia city, Bulgaria and in separate sampling points in the water supply network. Cluster analysis is performed for multivariate data interpretation of the distribution of aluminium (Al) concentrations during 2019 at 19 water sampling points (2 DWTPs outlets and 17 points within the city water supply system). Although the concentration of aluminium in the outlet of the treatment plants differ significantly, both of them fall into the same cluster, as the concentrations during the year change in the same manner. The formed cluster of both the treatment plants and most of the studied sampling points indicate the mixed origin of the purified water and proves that the concentration of Al in tap water is dominated by the qualities and quantities from the different sources of the supplied water, rather than by the secondary processes in the network for areas with predominant steel and polyethylene pipes. A distinct exception are the areas with old asbestos cement pipelines where potential release of the metal from the cement affects the Al distribution in the water supply system.