Water quality data at several sampling stations in Kofu for 30 years was analyzed and effects of enlarging sewered area on river water qualities were studied. Correlation between water quality variables was presented. As an attempt to show an overall trend in water quality variation principal component analysis was carried out. Three principal components were obtained. They may represent (a) overall intensity of water pollution, (b) balance between dissolved and suspended matter, and (c) temperature related index. The component representing overall intensity of water pollution has a close correlation with the enlargement of sewered area. The effectiveness of measuring more than one water quality variable in assessing water quality trend was pointed out. It was suggested that improvement in river water qualities with the enlargement of sewered area does not proceed to cleanness of upper streams.
