Abstract: The size and distribution of the population are crucial factors determining the demand for water resources. Considering the significant decline in total population growth, the evolution of China′s economic and social water demand is directly related to macro-level decision-making in water resource management. By analyzing the demographic composition of China′s population in terms of urban-rural distribution and age distribution, this paper clarifies the impacts of these factors on economic and social water demand. It further establishes a water demand change curve based on these demographic characteristics, which is used to predict the evolution of economic and social water demand trends and peak projections. The research findings indicate that the peak projection of China′s economic and social water demand may occur in 2042, reaching an estimated scale of 730 billion cubic meters; before 2050, the total water demand in urban areas will continue to rise, whereas the peak projection in rural areas will likely occur around 2030. The scale of economic and social water demand is a boundary condition determining the characteristics of regional water usage. As China′s economic and social water demand is yet to reach an inflection point, and as the international trade environment is becoming more volatile, future efforts to ensure water supply security in China should maintain a certain degree of flexibility and resilience.