Water quality index is one of the most effective tools to communicate information on the quality of water to the concerned citizens and policy makers. In this study, an attempt has been made to assess the water quality of Tigris River within Baghdad using the overall Index of Pollution (OIP) for surface water and examine the applicability of OIP for Iraqi water bodies by comparison the results with previous
scientific studies conducted for the same river. Twelve parameters were considered for estimation of OIP in Tigris River. It was found that mathematical equations given by OIP developers to estimate the index does not give a precise calculations, therefor,Microsoft excel (2010) for windows was used to extract value function curves for the
individual parameter. According to OIP, the river water is heavily polluted at Al-Doura WTP and Al-Rasheed WTP and the total coliform bacteria (TC) was the major factor that affects the quality of the river. Based on previous scientific studies, it was noticed
that the OIP is not quite applicable in assessment of Tigris river quality and even the previous studies that were conducted for the same river and used different water quality indices, it was found that some contrarieties and variations in the results of these studies when compared between each other. Therefore, develop a unique water
quality index applicable to Iraqi water bodies is of a prime importance.