Water network synthesis has been used to conserve water resources and reduce freshwater costs. However, a mathematical optimization model to maximize the profitability of a water network system has not been developed. The objective of this work was to develop the model to synthesize an economically friendly water network system by maximizing its net present value (NPV). The mathematical optimization model includes principal contributors to incremental costs and benefits resulting from water network synthesis. Tradeoffs between the incremental costs and benefits derived from water reuse are optimized to maximize the NPV. In a case study, an NPV-maximized water network system was more profitable than the total freshwater flow-rate-minimized and total freshwater cost-minimized water network systems. The model can be used to practically implement water network systems and can be applied to other process integration technologies to generate economically friendly heat and hydrogen network systems.