Abstract: The BeiDou Navigation Satellite System is a crucial spatiotemporal infrastructure of our country, which has been widely applied in various socio-economic fields since its establishment. Smart water sector is the most significant hallmark of high-quality water sector development in the new stage and one of the six implementation paths. The BeiDou system provides strong technical support for smart water sector and offers important spatiotemporal benchmarks as well as high-precision positioning and communication services for the construction of digital twin water sector. This article analyzes the current applications of the BeiDou system in typical scenarios such as water project deformation monitoring, water sector inspections, and the transmission of hydrological monitoring data from the perspective of the system's functionalities. Additionally, the article discusses the application of BeiDou remote sensing technology in water level monitoring, soil moisture inversion, and atmospheric water vapor inversion. Finally, this article outlooked the development trends of the BeiDou system in the field of water sector, noting that its application scenarios and fields will continue to expand, the scale of application will keep growing, and the integration with new technologies will increasingly strengthen. With the continuous innovation of the BeiDou system technology and the further expansion of its application scope, the BeiDou system will play an increasingly important role in the future water sector. It will become a vital force in accelerating the new quality productivity of water sector and promoting the high-quality development of the water sector.