Understanding how much water is used by ecosystems (through a process called evapotranspiration or ET) is important for managing water resources and assessing drought impacts. Scientists often rely on satellite data to estimate ET, but these estimates come from complex calculations rather than direct measurements. In our work, we used an alternative method based on the water balance—which looks at river flows, rainfall, and changes in total water storage—to calculate long-term ET for several river basins. When we compared our water balance results with the satellite estimates, we found that the satellite methods did not show the same variations. This means that while satellite data are useful, they might miss important details about how water use really changes over time. More work is needed to improve these satellite-based ET estimates so that they can better capture these critical variations.