Abstract: Accurate and reliable forecasting of economic and social water demand is a solid foundation for planning and constructing national water network projects. Current forecasting practice for economic and social water demand in China faces substantial challenges such as large computational errors and a lack of consensus about future trends. These difficulties stem from the limited recognition of the real obstacles in economic and social water demand forecasting, unresolved scientific questions, and unclear research priorities. This paper identifies five constraints: the complexity of multifactor coupling, the volatility of policy interventions, the subjectivity of calculation methods, the limitations of long-period forecasting, and the phenomenon of uncertainty. Then, it discusses three major scientific questions that must be resolved in economic and social water demand forecasting. Finally, driven by the practical needs of national water network planning and construction, this paper proposes four key research directions: the co-evolution mechanism between water resources and the economy and society system, interactive effects of water demand on the production and consumption sides, integration of forecasting techniques and methods, and estimation of medium- and long-term water demand along with uncertainty management. These findings provide theoretical support for decision-making in water resource management of China and for planning and constructing national water network projects.