Water availability to plants is one of the most important drivers of plant ecology, from species distribution to ecosystem functioning. This availability is defined by water input (via precipitation), water loss (via evapotranspiration), and, critically, water retention and storage (given by soil properties and topography). The large majority of studies of plant ecology focus on the first two drivers, which compose the climate, but tend to overlook the local water availability modulated by soil and topography (as might be captured, for example, in the water table depth, a key index of local water availability). Here we show how this hydrological component determines several patterns of plant distribution, acting as a filter of plant traits and thus affecting forest structure, composition, dynamics and ecosystem functioning. We show and discuss how this hydrological component is key to understanding forest responses to drought, from individual and population responses to canopy productivity. Last, we propose a theoretical framework on how to include this neglected factor in modeling of Amazon basin-scale forest responses to drought. This symposium is intended to be a synthesis of knowledge accumulated in the last 15 years of extensive and intensive work on gradients of water table depth in the Amazon. The perspective offered by this work suggests that water table depth can be an important filter of plant species and traits, which interacts with local hydrological properties to determine the impacts of droughts. Interestingly, the evidence suggests that in shallow water table depth forests, where there is frequently an excess of soil water that causes anoxic soil conditions, moderate drought conditions may enhance tree growth. This challenges the perspective of widespread and ubiquitous negative effects of climate change associated droughts on Amazonian forests, and may reconcile the contrasting reports of decreased productivity in deep water table biased forest plot networks and increased canopy function metrics observed with remote sensing, which capture shallow and deep water table forest regions. Furthermore, while some drought conditions may enhance growth in shallow water table depth forests, these forests also lack drought resilient functional traits, suggesting there is significant limitation to the resilience of these forests that has yet to be resolved. With the Amazon basin comprising up to 50% shallow water table depth forests, predictions of the impacts of climate change based largely on uplands with little access to soil water storage are likely inaccurate.