Determining the changes in the urban water footprint (WF) of the Tibetan Plateau is important for sustainable development within this region and in downstream regions. Taking Xining, the largest city on the Tibetan Plateau, as an example, this study quantified the changes in the WF of this region in the 2005–2018 period. We found that Xining’s total WF increased by 22.6%, from 8.9 billion to 10.9 billion m³ in this period. The increase in Xining’s gray WF (WF_gray) resulting from the intensification of urban point-source pollution was the primary cause of the increase in its total WF. Xining’s WF_gray from point-source pollution increased by 75.3%, from 3.1 billion to 5.4 billion m³. In addition, Xining’s WF far surpassed the amount of available water resources (W_A) in this region. It is possible to prevent Xining’s WF from exceeding its W_A only by simultaneously controlling point- and nonpoint-source pollution in the future. Thus, it is recommended that great importance be attached to the rapid increase in the WF_gray of the Tibetan Plateau resulting from rapid urbanization and that effective measures be implemented to control point- and nonpoint-source pollution, so as to safeguard sustainable development within the Tibetan Plateau and in downstream regions.