Although advances in water treatment technology have contributed to improved water quality at water treatment plants, treated water is not reaching consumer taps with the same quality. Water quality in service pipes is lower than at the water treatment plants, most likely because rust corrosion particles are generated inside the pipes, accumulated sediments become resuspended or other reasons. In this study, particles suspended in treated water flowing through water mains of various service areas were collected, and their quantity and elemental compositions were analyzed to investigate changes in suspended solid (SS) characteristics over distance and time. In addition to longitudinal changes along water mains, cross-sectional SS changes were investigated by developing a method of directly collecting SS particles flowing through a water main at different vertical locations. SS concentrations and the percentages of inorganics and iron in SS increased as water traveled toward the dead end of a main. Vertical differences of SS in the main cross section were also observed: SS concentrations in the upper part were higher than those in the middle and lower parts. The higher percentages of inorganics and iron in the upper part suggested that scaling in the upper part of the main, which had a stagnant area, caused iron particles to be released into the stream. Temporal variations in SS concentrations were observed for water flowing through the middle and lower parts of the main cross section. SS concentrations increased with increased flow rates, indicating resuspension of sediment at the bottoms of the mains. Overall, SS concentrations, their temporal variations, their cross-sectional changes and the elemental compositions of SS in water were different in various water service areas, and these characteristics could be useful in determining the origin of SS particles in drinking water.

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