This study focuses on the assessment of existing drinking water quality in Adama Town, whichrnis located in East Shoa zone; it is found in the administrative of National Regional state ofrnOromia. It is far from Addis Ababa 100km on the old asphalt high way road to Harar.The townrngets its Water supply from a treatment plant.The two consequential methods were used tornachieve these objectives.The first method in volved the collection of samples from differentrnlocations of the study area followed by laboratory analysis, and the Second method in volvedrnthe use of simulation models such as Epanet Software to identify the pressure effect on residualrnchlorine in the water supply gravity distribution network system.For bacteriological analysis,rnthe whole 45 representative samples were randomly selected from sensitive areas for expectedrnpollution such as raw water, treatment plant ,service reservoir, water points, ends of pipernnetwork, Sensetive points and customer point of user, and 45 samples were used for physicochemicalrnanalysis. The results obtained show that Iron concentration is equal to World HealthrnOrganization permissible limit.The residual chlorine was zero in 45 samples except Kokarntreatment plant on frist round sample taking and laboratory test results. But after Constant-rnHead drip chlorinator on Lugo reservoirs and taken sample second round and test inrnlaboratory the results of residual chlorine give us 0.02-0.3mg/l at the consumerâ€™s water taprnand at reservoirs get 0.8mg/l residual chlorine.The results of Color concentration during Wetrnand Dry seasons were found between the ranges of 9-17 TCU.This result is greater than WHOrnmaximum permissible limit values and less than Ethiopian maximum permissible limitrnvalues.The majority of samples less than the maximum World Health Organization andrnEthiopia permissible limit.the result of bacteriological analyses indicated that in most of thernsamples no risk was observed after construct temporary Constant-head drip chlorinator. Forrnfuture parmenently chlorination is recommended at Lugo reservoirs. The simulation resultsrnshowed that the pressure has inversely relationship with the residual chlorine in the distributionrnsystems of the networks.rnKey words: - Water quality Modeling, GIS, GPS, Global Mapper, Epanet, Physical,rnChemical, Bacteriological, Adama Town Water Supply