Abstract: Managing the water cycle to achieve sustainability goals requires understanding how dynamic processes that may respond to change impact water balance over scales on which water resources accumulate. In recent years, the application of isotope tracers to study water flow through the Critical Zone has provided support for the long-standing concept that the movement of water through soils is heterogeneous, and hinted that this heterogeneity may have important implications for the fate of precipitation delivered at different times. I will present three studies, spanning scales from individual soils to the globe, suggesting that the bifurcation of the water cycle within soils, also known as the ‘two water worlds’ hypothesis, exerts real and detectable influences on the structure of water flows through terrestrial hydrological systems. This concept provides dynamical links between soil structure, climate variability and extremes, and water resource quantity and quality that need to be better defined and represented in models of future water cycle change.