Study region: The arid region of northwest China Study focus: Intense evaporative losses threaten the construction and safe operation of pumped storage plants (PSP). To address the issue of rapid water level fluctuations in the upper and lower reservoirs, floating ball coverage technology is one of the ideal measures to reduce reservoir surface evaporation. However, the upper and lower reservoirs of PSP are located in different meteorological environments (with high water heads), and their characteristics such as frequent mutual exchange of water bodies and their heat, as well as frictional heating between water flow and units, result in a significant difference in the evaporation calculation model compared with traditional single reservoir. This study integrates the operating conditions, meteorology and ball properties into the model, which is applied to evaluate the water-saving effects, and potential benefits of floating ball coverage on the reservoirs. New hydrological insights: The results show that: when the floating ball coverage rate is 74%, the water-saving effect of the reservoirs reaches 61.2%. The simulation results are consistent with the observation data from field tests of small evaporation ponds. Furthermore, the water temperature drop rate of the covered reservoirs is significantly reduced, which can effectively inhibit water freezing in winter. This study can provide a reference for the planning, design, and safe operation of PSP in arid regions.