Using field studies on sewage flows and Infiltration/Inflow(I/I) analysis in separate sewer systems, the appropriate I/I values were computed, and an alternate method of calculation for I/I was presented. Sewage flows followed a typical diurnal pattern with highs in the morning and evening and lows during the night. The BOD concentration of sewage ranged from 200 to 400mg/L. Diurnal variations in BOD concentration fell slightly during the night, when there were low sewage flows. This is likely the result of dilution due to the inflow of groundwater, but it was difficult to quantify the effect. The infiltration varied considerably in the data, from -14.8% to 14.0% of the daily maximum sewage flow. This is due to the limitations of the method of calculations rather than errors in measurement. In short, the method of calculation for night-time domestic flow only takes into account the population of a particular region. Therefore, if the characteristics of night-time activities of residents are different, the method is unable to reflect it. As such, the method of calculation should be updated with continued research. Analysis of the inflow showed that the specific inflow rate was 0.7 to 2.7m 3 /min, lower than the results of similar studies. The values were higher for regions where the pipe lengths were longer and had a larger number of house-inlets.