In this study, different guidelines have been determined in many legislations for the evaluation of drinking water of Lake Aygır in Bitlis. In monitoring water quality, CWQI was chosen as a model. In this model, the guideline values in Turkish national legislation, which determine the quality of drinking water, are used. Selected legislations: "Regulation on Water for Human Consumption", "Water-Water for Human Consumption", "Regulation on Surface Water Quality Management", "Regulation on Quality and Purification of Drinking Water Supply Water" and their index values are 86.21, 86.23, 88.88 and 84.71 respectively. CWQIASQ-Y has been determined as 72.48 and CWQIASQ-M has been determined as 81.75 within the “Regulation on the Amendment of the Surface Water Quality Regulation”. Lake Aygır waters are classified in medium quality according to CWQIASQ-Y and in good quality according to all other guidelines.