The objective was to determine impact factors that would allow Pseudomonas aeruginosa and Legionella pneumophila to survive sanitation measures of household drinking water systems. Therefore, different disinfectant concentrations were tested under different operating conditions in close-to-practice experiments. Particular attention was paid to the viable but non-culturable (VBNC) state of the pathogens. Legionella pneumophila was able to survive disinfection with ClO2 in a culturable state in the biofilm at 37 °C while successful sanitation could be achieved at 11 °C, however non-culturable cells were still present. Culturable P. aeruginosa outlasted disinfection in biofilms of pipes at elevated nutrient concentrations and in built-in parts at 37 °C. Overall, the VBNC state was not the predominant factor for its survival. Additional experiments showed that the lack of an autochthonous biofilm may promote the growth of P. aeruginosa. This emphasizes the importance of localization and elimination of contamination sources in a plumbing system before disinfection is performed and the need for compliance with operating conditions and construction requirements defined by generally recognized standards of good practice in Germany.

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