The water-phosphorus nexus problem for wet-process phosphoric acid production is first addressed in this article. A systematic methodology for water system optimization and water-phosphorus nexus analysis is proposed. On the basis of the preliminary process flowsheet and water flow rate balance, the potential water sources and sinks as well as the key component can be extracted. The mathematical model for the water system optimization integrated with water flow rate balance is presented. The process flowsheet can be improved according to the optimized water system. The flow rate of fresh water is reduced from 1803.98 t/h (preliminary design) to 160.98 t/h (improved design). The utilization efficiencies of the phosphorus element (calculated as P2O5) are calculated for the preliminary and improved designs. Because the process for wet-process phosphoric acid production is mostly in the aqueous phase, the utilization efficiency of the phosphorus element is increased from 94.22% (preliminary design) to 98.76% (improved design) due to the reuse and recycling of water stream with the phosphorus element. Water minimization and phosphorus recovery can be achieved simultaneously. The additional annualized profit for the improved design reaches 248.8 X 10(6) CNY/a, which is a great benefit for the production plant.