Estimates of maximum crustal water inventory from back-of-envelope calculations. The maximum depth is calculated where the geothermal gradient intersects the dehydration temperature of serpentine, and where the lithostatic pressure intersects the dehydration pressure of serpentine (Equations (A1)–(A6)). Crustal hydration is limited to ∼0.1% of an Earth ocean (10¹⁸ kg), and ∼10% of an Earth ocean (10²⁰ kg).