A water reservoir located approximately 700 kilometers below Earth's surface contains more water than all of Earth's oceans combined.

Caveats

• The 'more than all oceans' volume is a theoretical maximum based on an assumed 1% water content in mantle rock — not a measured or confirmed quantity. The most rigorous scientific synthesis estimates only 0.2–1 ocean equivalents in the transition zone.
• The water is not liquid but chemically bound as hydroxyl radicals within minerals like ringwoodite — calling it a 'reservoir' or comparing it directly to ocean water is fundamentally misleading without this qualification.
• Multiple media sources repeat the same conditional estimate from a single underlying study, creating an illusion of independent corroboration when the evidential base is narrow and consistently hedged with words like 'may,' 'potentially,' and 'if.'