The regulation of Earth’s climate and its ability to sustain life are critically linked to water as it exists in all three of its phases (gas, liquid, and solid). Earth’s water cycle, its movement between the hydrosphere, biosphere, and the atmosphere, and how it undergoes phase changes, is incredibly complex. While we continue to gain insight into the water cycle, there remains considerable uncertainty in predicting the impacts of future climate change on fresh water supplies and the welfare of life on our planet. This uncertainty exists, in large part, because of a scarcity of highly-resolved spatial and temporal observations of Earth’s hydrology. One proven tool for observing the dynamics of the water cycle is stable isotope analysis of water. Differences in the thermodynamic properties of the isotopologues of water lead to differences in the isotope ratios (18O/16O and D/H) in different environmental water reservoirs. The differences in isotope ratios, in conjunction with meteorological observations, can be used to trace water as it is cycled, and to characterize and identify condensed water sources. Recent advances in cavity ring-down spectroscopy (CRDS) have led to field-deployable instrumentation capable of making real-time high-throughput stable isotope measurements of water. Furthermore, the high precision of such instrumentation (typically < 0.2 ‰ for D and < 0.07 ‰ for 18O) allows for high-resolution measurements that enhance our understanding of the processes that govern natural variability in water isotopes. This presentation demonstrates the results from two different applications of the Picarro isotopic water analyzer. First, the analyzer was used to measure vertical gradients in ambient water vapor isotopes at Blue Oak Ranch Reserve, CA. The Picarro analyzer was deployed with Picarro’s new Standards Delivery Module, a novel, field-durable and automated calibration system that introduces liquid water standards, as vapor, without fractionation effects. The results show clear gradients in water vapor isotopes during cooler nighttime periods, which subsequently break-up during daytime warming. The second set of results show measurements of liquid water samples collected from three different watersheds at Mammoth Lakes, CA. The data are comprised of samples collected from thirty different locations including snow melt lakes, creeks and rain water. The isotopic measurements shed some light on the dominating hydrological phenomena which affect the isotopic content of the water. However, and more importantly, the data demonstrate a complex relationship between the hydrological cycle, volcanic activity and hot springs contributions, and illuminates the fact that a simple explanation involving fractionation along water courses is not sufficient.