Comment Not so fast (Score 1) 2
Rare Diamond Confirms That Earth's Mantle Holds an Ocean's Worth of Water (Scientific American, March 12, 2014) says:
The ringwoodite is 1.5 percent water, present not as a liquid but as hydroxide ions (oxygen and hydrogen molecules bound together).
It goes on to say
The results suggest there could be a vast store of water in the mantle transition zone, which stretches from 254 to 410 miles (410 to 660 km) deep.
It's not clear from the article if there is any actual H2O or if it's all OH-. If it's all OH-, it's not clear where the extra proton went.