This paper presents a new approach to targeting minimum freshwater and minimum effluent treatment flow rates of a water allocation network.A grand composite curve based on the concept of Wang and Smith’s limiting composite curve was constructed firstly to determine the waste water line with minimum flow rate.Then

the waste water line was modified for the case of regeneration-reuse.The minimum treatment target was obtained through a waste water composite curve

which was generated from the grand composite curve.The proposed approach could be applied to the fixed flow rate as well as the fixed contaminant load problems with a single contaminant.Finally

the reuse

regeneration-reuse and waste water treatment problems could be solved in a single concentration versus contaminant load diagram.