Stable isotope ratios of meteoric water are incredibly useful for determining all sorts of hydrologic parameters. NASA’s Science Mission Directorate’s focus area on studying climate-driven changes in the water cycle can benefit greatly from stable isotope studies, as stable isotope tracers may elucidate even the most complex of hydrologic processes. Beyond water, stable isotope ratios in sediments can be used to study environmental pollutants. Here, we begin with a brief background of how stable isotope geochemistry works before discussing three common applications that are related to NASA’s Science Mission Directorate’s hydrology focus. These three subjects are hydrologic catchment dynamics, flood risk assessment, and limnology. For limnology, a case study is provided for Sturgeon Lake on Sauvie Island, Oregon. We explore some current problems related to studies of the water cycle and propose ways that stable isotopes could be used to either solve the problem or deepen our understanding. For the sake of this paper, the problems we focus on are centered around the Pacific Northwest. We show that stable isotope tracers are vital to studying the influences of climate change and anthropogenic influences on the water cycle, allowing a better understanding of how Earth’s water systems will change and what we can do to mitigate potential harm.