There are multiple distinct habitats for microbiota inhabiting the plant microbiome (phyllosphere, endosphere, litter, rhizosphere) and habitats that act as additional sources (and sinks) of microbes and nutrients for the plant microbiome (atmosphere, pedosphere, bedrock, and fauna). These habitats harbor distinctive microbial communities that differ in structure, composition, function, and spatiotemporal dynamics. Each habitat also differs in the mechanisms that provide “gateways” of exchange of microbes (and microbial products) between two communities, or in their access to “highways” that connect multiple communities. Of the environmental processes driving microbial community exchanges, precipitation events seem to represent the only one highway that can connect all the abovementioned habitats—the “hydrologic highway”. When precipitation contacts plants, it is partitioned into interception (water stored on, and evaporated from, plant surfaces), throughfall (water that drips from canopy surfaces and through gaps), and stemflow (water that is drained down the stem). This chapter describes the ways that precipitation partitioning in vegetated ecosystems (into interception, throughfall, and stemflow) may connect microbial communities from the top (atmospheric boundary layer) to the bottom (bedrock face) of the critical zone via these hydrologic highways.