One can assess the quality of water by water quality index method and it is a mathematical method to evaluate the water quality based on physical or chemical parameters, using WQI one can evaluate the water quality of both ground water and surface water, while determining the WQI one can use the standards or guidelines provided by some standard organizations like WHO (world health organization), National Standard Body of India (BIS), ICMR (Indian Council for Medical Research) etc. To assign grade to the water samples under study, apart from the WQI there are some other popular techniques used to evaluate water quality they are statistical methods, multivariate statistics, neural networks, fuzzy logic and machine learning algorithms. The aim of this study is to give insight into various methods used or developed to evaluate water quality of both ground and surface water by earlier research works.