There are several factors influencing the water quality based on its usage. The quality of drinking water is of the vital concern for human health and life. An essential attempt has to be done to develop a water quality index (WQI) corresponding with different conditions and characteristics of the relevant river or water body such as geographical, hydrological, discharge rate and pollution sources. The index is not specifically focused on human health or aquatic life regulations. However, a water index based on some very important parameters can determine a simple indicator of water quality. In the present study, the Gorganrood water quality has been evaluated by available NSF water quality index. Subsequently, the nine present NSF parameters’ weights have been changed and modified using the analytical hierarchy process (AHP) method as well as experts’ opinions in the field in a way to satisfy local conditions. In the newly developed WQI, more weights are given to relation with these parameters it can be said that the factors like dissolved oxygen (Do), fecal coliform (F.c) and biological oxygen demand (BOD) when compared with NSF-WQI.