Biofilms are surface-associated bacterial communities that predominate in natural and pathogenic ecosystems. Their formation in drinking water systems creates potential risks for consumers’ health. Herein we tested biofilm formation on materials commonly used for indoor household drinking water systems (copper, PVC and stainless steel) simulating an average family water usage. Water parameters were determined by standardized methods while biofilm formation was assessed by epifluorescent and laser scanning confocal microscopy, for determining the numbers of attached cells, biofilm thickness, colony size and average colony surface. Results showed a very fast colonization on all materials used, of log 6–7 cm−2 cells disposed on a single layer on copper and PVC. On stainless steel, beginning on the 24th experimental day, there were observed multiple layers of cells and a rapid increase of biofilm thickness. The lowest overall number of attached cells was found on copper. Microorganism colonization and biofilm formation is possible and quite fast on an indoor water system connected to a chlorinated water network. From the tested materials, the greatest risk to consumer health comes from biofilm formation on stainless steel parts which are used in the very large majority of residences.

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