The researchers studied the water quality changes in the distribution systems of water treatment plants in Jeju City. They collected and analyzed water samples monthly for a year. The levels of nitrate and chloride in treated water stayed fairly consistent but varied with the seasons. The pH of the water changed slightly in some plants, while turbidity was mostly stable. Residual chlorine levels were affected by the storage tank's residence time. Cancer-causing compounds in the water were below safety limits, but levels increased in water that had been stored longer.