The reservoir water quality of Maithon reservoir was analyzed by using the method of Multivariate-statistical-techniques. Water samples were collected on bi-monthly basis from four different sampling stations along the longitudinal gradient of the reservoir by considering a time frame of 1.5 years. The output results were compared with the international and national water quality criteria. Study demonstrates the application of various statistical techniques like Principal Component Analysis (PCA)/ Factor Analysis (FA), Pearson Correlation Index (PCI) and Cluster Analysis (CA). PCA/FA identified five principal components (factors)in the entire dataset explaining 86.443% variance in the dataset for the Riverine-Zone (RZ), 85.589% variance for the Transition-Zone (TZ), 80.859% variance for the Lacustrine-Zone (LZ) and83.391% variance for Down-Stream(D/S) zone. The Water Quality Index (WQI)was also computed to know the overall quality of the reservoir water for various purposes (domestic purpose, industrial purpose, irrigation purpose etc.). The value of overall WQI computed was 40.22 which reveal that the reservoir water falls under good category. This study suggests the applicability and necessity of multivariate-statistical-techniques for analyzing and interpreting vast and complicated data sets, with an eye on improving the water quality and creation of monitoring networks for the efficient management of water resources.