ABSTRACT The treated water by reverse osmosis is widely used as one of the types of drinking water, and for the correlation of this water with the health of individuals, this study was aimed at detecting the bacteriological quality of this water. Samples were collected based on three drinking water supply stations using reverse osmosis system . three samples ( from the same station ,from water seller that supplied by station water , from houses that supplied by station water ) were collected per station per month, for the period from November 2017 to march 2018 .The bacteriological analyses were Heterotrophic plat count (HPC) ,Total coliform (TC) count and E.coli count . It was appeared , the high rates of numbers of HPC in all stations ,they registered 190 ,70 and 5×102 ( CFU / 100 ml). The rates of total coliform (TC)from same stations , as it reached 0 , 67 , 2×102 (cell / ml ) in stations respectively , houses recorded the highest rates of these bacteria for all stations 53 , 100 , 4 ×102 ( CFU / 100 ml) in A , B and C respectively . The rates of E.coli in RO treated drinking water samples that collected from the same stations were 0, 13,1×102 ( CFU / 100 ml). The higher numbers of E coli were appeared in houses for all stations , it registered 50,27 and 4 ×102 ( CFU / 100 ml) for stations A ,B and C respectively . Numbers of these indicators in most samples of RO treated drinking water exceeding the international standards. the number of bacteria that isolated from these water were 36 isolates that distributed to 27 ( 75%) Gram negative and 9 ( 25% ) Gram positive bacteria ,Klebsiella spp. was the more frequency isolate among Gram negative bacteria , and Enterococcus fecalis was the predominant among Gram positive bacteria.