This study analyzed 323 water samples from 178 buildings in Taipei, Taichung and Kaoshiung cities to evaluate the water quality deterioration after roof-top storage. Water quality in distribution systems, household intake tanks (point-of-entry) and the tap (point-of-use) were compared. It was observed that chlorine decay is the major factor in deteriorating the water quality after storage. Relatively high water temperature and the presence of higher organic/inorganic impurities are the main reasons that cause the large chlorine decay in Kaoshiung. Most of the microbial regrowth was observed in the samples with chlorine residuals less than 0.2 mg/L, indicating that 0.2 mg/L of chlorine residual is a suitable criterion to prevent the microbial contamination. After roof-top storage, the chlorine residual, total dissolved solids and turbidity were decreased; however, total bacteria counts and pH were increased. For better management of household storage systems, some preventive actions has been taken to improve the water quality at point-of-use.

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