In order to design and operate an effective water treatment system, a thorough understanding of the process of coagulation-flocculation and filtration is essential in the delivery of water of the greatest clarity and lowest possible turbidity in the finished water. This research outlines the finding of investigation of the treatment plant in Al-Dewanyia in Iraq. Performance of Al-Dewanyia Water Treatment Plant in Iraq is an essential parameter to be monitored and evaluated to better understanding of design and operating difficulties in water treatment plants. The conclusions of these evaluations may determine required recommendations and highlight modification requirements for continuous design and operating schemes. The evaluation conducted in this research was carried out by reviewing the engineering design to assure matching of standards and codes. Also, physical (turbidity and TSS) , and biological, analysis were conducted to investigate water quality. The conclusions drawn from this research outlines the importance of accurate engineering design and need for continuous monitoring and analysis of each unit performance. Finished water is not conforming to World Health Organization (WHO) Standard for Drinking water.