Abstract: A continuous-flow system is described and illustrated, for simultaneous determination of chloramide (I), chlorimide (II) and free Cl in water, which incorporates three double-tube separation units, each consisting of a PTFE outer tube and an inner tube of micro-porous PTFE. The three tubes were used for determination of I, I plus II, and I, II and Cl, respectively, by reaction with I- and absorbance measurement at 288 nm. Optimum pH and reagent concentration. for each reaction are given. Calibration graphs covered the ranges from 0.1, 0.02 and 0.02 mg L-1 of Cl for I, II and free Cl, respectively, to 71 mg L-1 for all Cl species. Within- and between-run coefficient of variation were 3.3% (n = 5) and 10% (n = 8), respectively. The method was applied in monitoring of I and II in water purification plants.