Water is life, but for all its importance, humanity has a surprisingly limited view of Earth's freshwater bodies. Researchers have reliable water level measurements for only a few thousand lakes around the world, and little to no data on some of the planet's important river systems. The upcoming Surface Water and Ocean Topography (SWOT) satellite will fill that enormous gap. By helping to provide a better understanding of Earth's water cycle, it will both aid in better management of water resources and expand knowledge of how climate change affects lakes, rivers, and reservoirs.