Introduction: Drinking water should not pose a health risk to humans. It is necessary to provide medically appropriate drinking water in the entire water supply network all the way to the end user. Regular maintenance of the internal water supply network is important in order to maintain previously healthy drinking water. Purpose: The purpose of the master's thesis is to check whether the stagnation of drinking water in the internal water supply network causes an increase in the concentrations of zinc, lead and iron, and whether these concentrations can be reduced by flushing the internal water supply system. Methods: The master's thesis uses a descriptive method with a critical analysis of domestic and foreign literature, a review of the results of already performed sampling and analysis of drinking water at various facilities, before and after the flushing of the internal water supply network where the trend of passing metals into the internal water supply network was shown. We carried out five samplings and analysis for the presence of zinc, lead and iron in the selected facility before and after flushing the internal water supply network. Results: With the collected results of previous samplings in various facilities we obtained information that by flushing the internal water supply network, the exceeded limit values of zinc, lead and iron can be reduced to below the limit values. By sampling and analysing the drinking water in the selected facility, we found that 48 hours of stagnation of drinking water in the internal network is enough for the concentration of zinc and iron to exceed the limit values. Zinc values were elevated, but limit values were not exceeded. By flushing the internal water supply network in the selected facility, the exceeded limit values were reduced to extent that the samples were compliant with the provisions of Uredba o pitni vodi. Discussion and conclusion: With the collected data of previous samplings and the results obtained through sampling and analysis in the research we can conclude that the flushing of the internal water supply network is important from the point of view of exceeded limit values of zinc, lead and iron, which appear in drinking water in the internal water supply network. We found that by flushing the internal water supply network, we successfully reduced the exceeded threshold values of the analysed parameters, so it would be important to raise awareness of the importance of flushing internal water supply systems after a long period of water stagnation to the general public.
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