The conventional water treatment plant, especially in developing countries, faces majorrnchallenges in terms of assessing its operation and performance due to inappropriaterntechnologies, insufficient equipment and deficiency in skilled expertise. Simple but efficientrntechnologies are therefore necessary for reasonable evaluation of the daily performance ofrnthe plant. Turbidity is thought of as a convenient surrogate to give favorable indication of thernbiological and physical quality of the treated water thus by extension provide a fair gauge ofrnthe performance of the treatment plant with respect to water purification. Besides, it is fairlyrnsimple to measure, cheap and can easily be understood by the operators. In this study thernperformance of Gambella town water treatment plant was assessed. The study was conductedrnby assessing unit process capability, design, operation and maintenance potential to meetrnoptimized goals. From results of the assessments, root factors limiting optimum performancernwere identified and improvement options were proposed. Major unit processes werernevaluated to project their design capabilities to meet current peak water demand by selectingrnappropriate loading rates as basis criteria. The results of the assessment found that all unitsrnhad the capability to satisfactorily treat water at peak daily demand of 2000 mrn/day. Thernstudy assessed turbidity performances of sedimentation and filtration units by settingrnoptimized turbidity goals. The assessment results indicated that, settled water turbidity wasrnmeasured less than 10 NTU. And filter turbidity spike of 6.5 NTU following backwash withrna reduction to 0.6 NTU after one hour was observed. Generally optimized performance goalsrnwere not being achieved. This indicated high risk of microbial pathogens that could pass thernfiltration barriers in the finished water. Jar test experiments were conducted to evaluate therneffectiveness of Aluminum Sulphate (recently used by the treatment plant), Ferric chloridernand Ferric Sulphate by comparing the optimum dose at optimum pH for highest turbidityrnremoval and relative costs. From the jar test results Aluminum Sulphate was found to be therneffective chemical with 45 mg/l optimum dose at pH 7.1 and the treatment plant wasrnrecommended to continue using Aluminum Sulphate at the optimum dose for the raw waterrncharacteristics during the evaluation period. Treated water samples were collected from thernclear-water well to test 14 water quality parameters according to the standard methods forrnwater and waste water examinations. The collected samples were intended to show the characteristics of the finished water only during the evaluation period. The samples werernanalyzed at the laboratory of GWTP and results were compared with WHO standards andrnguidelines for drinking water. Results of the analysis showed that all of the measuredrnparameters were within the acceptable range. In the assessment of factors limitingrnperformance of the treatment plant; major factors were categorized as design, operational andrnmaintenance. No single factor was responsible for poor plant performance, although inrngeneral the study found that all factors influence the plantâ€™s ability to work properly. Some ofrnthe primary operational problems and the intake structureâ€™s adequacy significantly affectedrnperformance. Operational factors were found to have the highest rank. This finding, coupledrnwith the fact that the plant had adequate capability, indicates that improving process controlrncould significantly improve performance.