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The effect of stagnation on the concentration of heterotrophic bacteria and ATP in tap water from three office rooms, characterized by different water consumption pattern, was studied. From every room, the first liter of tap water in the morning after 18hours and 4days stagnation periods was sampled, as well 3L and 10L tap water after moderately flushing. Temperature, concentration of free chlorine, total adenosine triphosphate (ATP) as well as heterotrophic plate count (HPC) were measured immediatelly.
The lowest HPC and ATP concentrations in stagnated water were obtained from regularly used tap in office room. In other rooms, where water intake was less intense and occurred periodically, high HPC (105 CFU/ml) and ATP concentrations were detected in the stagnated water indicating the presence of active biomass, despite the free chlorine concentration of about 0.5 mg dm-3, and heterotrophic plate counts only slightly decreased after flushing of 10L.
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