The current study was conducted to assess the quality of treated water in the Dandan water treatment plant for drinking water and its related residential neighborhoods on the right side of Mosul city. Water samples were collected from ten sites (before and after treatment and the rest from the residential areas included in the study) to estimate the physical, chemical and bacteriological properties, the Organ Model (OWQI) was also applied to assess the quality of the studied water. The results of the study indicated the efficiency of the Dandan water treatment plant for drinking, where the water was of the type of excellent water after treatment, while the rest of the studied sites were of the category of excellent water quality to very good quality, as a result of the quality index values ranged between (88.74 to 91.7) This relative decline in water quality in some residential neighborhoods is due to the presence of fecal coliform bacteria in some periods. The study recommends educating the population about the harms of connecting water pumps directly to the distribution network pipes and applying deterrent laws to violators.