This study investigates the depth-dependent flux of water from subducting slabs worldwide. Using a global compilation of thermal structure models for subduction zones, the authors predict the metamorphic facies and water content of downgoing slabs. The results indicate that mineralogically bound water can efficiently pass through old and fast subduction zones, while hot subduction zones like Cascadia experience nearly complete dehydration. The top of the slab is sufficiently hot in all subduction zones to dehydrate the upper crust, including sediments and volcanic rocks. The degree and depth of dehydration in the deeper crust and uppermost mantle vary significantly and depend on composition and local pressure and temperature conditions. On average, about one-third of the bound water subducted globally reaches a depth of 240 km, carried primarily by gabbro and peridotite sections. The predicted global flux of water to the deep mantle is smaller than previous estimates but still amounts to about one ocean mass over the age of the Earth, increasing the overall mantle H2O content by 0.037 wt% (370 ppm). This is consistent with inferred H2O concentrations in the Earth's mantle, suggesting that secular cooling has increased the efficiency of volatile recycling over time.This study investigates the depth-dependent flux of water from subducting slabs worldwide. Using a global compilation of thermal structure models for subduction zones, the authors predict the metamorphic facies and water content of downgoing slabs. The results indicate that mineralogically bound water can efficiently pass through old and fast subduction zones, while hot subduction zones like Cascadia experience nearly complete dehydration. The top of the slab is sufficiently hot in all subduction zones to dehydrate the upper crust, including sediments and volcanic rocks. The degree and depth of dehydration in the deeper crust and uppermost mantle vary significantly and depend on composition and local pressure and temperature conditions. On average, about one-third of the bound water subducted globally reaches a depth of 240 km, carried primarily by gabbro and peridotite sections. The predicted global flux of water to the deep mantle is smaller than previous estimates but still amounts to about one ocean mass over the age of the Earth, increasing the overall mantle H2O content by 0.037 wt% (370 ppm). This is consistent with inferred H2O concentrations in the Earth's mantle, suggesting that secular cooling has increased the efficiency of volatile recycling over time.