The discovery of hydrous ringwoodite inclusion in diamonds with 1.5 wt.% H2O provided an irrefutable indication that water is present in the Earth's deep mantle. Whether this water was delivered by one of the numerous subducted slabs observed by seismological studies, or whether it appeared right after the crystallization of the Earth's mantle from a magma ocean, and the total budget of water in the Earth's interior are all still up for debate.