Water quality deterioration in surface water is the impact of anthropogenic activities due to rapid industrialization. Tigris River within Baghdad city is of particular importance in the study of surface water quality because; industrial and municipal wastes, agricultural and runoff from developing areas were mixing with river flow and surrounding water body thereby deteriorating the quality. The aim of the study was to assess the WQI on the basis of Weighted Arithmetic Index in order to evaluate the water quality of the Tigris River for drinking purposes from three stations within Baghdad city during 2013. The WQI was calculated based on the concentration of eleven parameters (pH, Total Dissolved Solid (TDS), Total Hardness, Calcium, Magnesium, Chloride, Turbidity, Nitrite (NO2), Nitrate (NO3), sulphate (SO4) and Zinc). The calculation of WQI showed that the water quality of Tigris river can be rated as very poor and unsuitable conditions at winter and summer, respectively, in the 1st site which is situated at the north of the study area while the water quality of the 2nd site can be categories as unsuitable conditions at all season of study and for 3rd site can be rated as poor and very poor conditions at winter and summer season, respectively. Therefore, there is need a regular monitoring of water quality in order to detect the changes in physio-chemical parameter concentrations.