Microbiological drinking water quality in a highrise office building of Hong Kong

Microbiological water quality of the drinking water is highly associated with enteric diseases. In this study, the water quality for the water supply system of a typical highrise office building in Hong Kong was examined. A comparison of the bacteria levels between the high and low water consumption periods was made. Tap water samples (0.1 L) were collected at the water supply system every 4 hours from 08:00 to 20:00 in a normal working day that had a working day prior and after and a normal working day that followed a long weekend. The results showed that the bacteria counts ranged from 80 to 1000 CFU L−1 . It was found that the bacteria counts at a time after a low water consumption period were significantly higher. This was probably due to the multiplication and accumulation of bacteria in the water storage system in low occupancy hours. Among the bacterial genera identified, 59% were gram-positive bacteria genera composed of Bacillus (6%), Micrococcus (28%), Staphylococcus (6%) and others (19%), and 41% were gram-negative bacteria genera including Pseudomonas (13%), Escherichia coli (1%) and others (27%). A low quantity of the faecal indicating bacteria, E. coli, was detected with a relative abundance of 0.5-1.4%. Its presence was probably due to bioaerosols generated from nearby WC flushing. Future investigations regarding the probable transmission through a water supply system of high-rise office buildings in sub-tropical climate were recommended.