Water quality of the river Cauvery and its tributaries -Arkavathi and Vrishabhavathi was assessed by using Bhargava's water quality index. Significant seasonal variation was revealed by the spatially measured physico chemical characteristics. The water quality index is categorized as class III (satisfactory range) for the Cauvery and Arkavathi rivers and class 4 (poor range) for the Vrishbhavathi. The spatial homogeneity of quality was determined by using Duncans multiple range test.