A systematic approach for wastewater treatment network (WWTN) design has been developed. The method is sequential and applies insight-based techniques followed by mathematical programming. Overall goal function is the sum of wastewater treatment cost and piping cost. The novel feature of the method is application of mathematical models of treatment processes. The approach has been applied to retrofit WWTN in various industrial facilities. In this paper, we address the example of designing WWTN for a synthetic organic dye manufacturing plant.