Performance limiting factors (PLFs) derived from 161 drinking water treatment plants (DWTPs), assessed by the International Technical Diagnosis and Assistance Center, were analyzed and evaluated in this study. In order to conduct research, 161 DWTPs were divided into five categories depending on their capacity, and into twelve groups according to processes and facilities. From the results of analysis, PLFs and their distribution ratio derived from each category were significantly different. Filtration was the most important performance limiting factor in all DWTPs of five categories, and PLFs in filtration were backwashing velocity, media configuration, bed depth, and formation of mud-ball. The PLFs in coagulation–flocculation process were found to be coagulant dose, mixing intensity, mechanical problems, and others in the order of frequency of occurrence. Also, insufficient disinfection ability, is resulting from insufficient hydraulic detention time, improper chlorine dose and injection point, is the most significant among PLFs in a clear well. In the case of sedimentation, inappropriate baffle structure and excessive upward velocity were PLFs. In addition, the results showed that high turbid water and low alkalinity in rainy season, ferric and manganese ions, and ammonia nitrogen have contributed significantly to the performance of DWTPs.

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