Introduction & Objective: Rivers are one of the main water supply resources for various uses such as agricultural, industrial and drinking purposes. As population and consumption increase, monitoring of rivers water quality becomes an important function of environmental management field. Because Darreh-Morad Beyg river of Hamadan is a water supply for different purposes and many pollutants are discharged in it, its water quality assessment seems necessary. Zoning of pollution and depicting a detailed image of surface water resources quality using geographic information system (GIS) are the key factors for the better management of these resources.

Materials & Methods: This research is a cross sectional- descriptive study and river water samples were taken for 7 months from 6 sampling stations on the length of the river. Biochemical oxygen demand (BOD), electrical conductivity, dissolved oxygen (D.O.), pH, fecal coli form, nitrate, temperature, phosphate and total solids were determined in the samples. Obtained data were analyzed by national sanitation foundation water quality index (NSFWQI) and the river was zoned using GIS software.

Results: Results of the analyses by NSFWQI showed the best water quality for station 1 and the worst water quality for station 6 with scores of 62.78 and 27.49, respectively.

Conclusion: The NSFWQI is a suitable index for zoning of Darreh-Morad Beyg river. Monitoring of physical, chemical, bacteriological quality parameters and using water quality index in various sampling stations are used in the assessment of water pollution. It also helps the officials to correctly decide about the water uses for different purposes.