If just 1% of the weight of mantle rock located in the transition zone was water it would be equivalent to nearly three times the amount of water in our oceans, Jacobsen said.
That isn't evidence of any free flowing water though or that there is that much water, it's pure speculation. The trick is the "if". Suppose I say:
If just 1% of the weight of rock located on the moon was gold, it would be equivalent to nearly three times the amount of gold in bank reserves.
Does this mean the moon is going to make us all rich? No.
You can condense it to something shorter that is nowhere near as convincing, but linguistically the same:
If there was 3 times as much water hidden in rocks within the earth as there was in the oceans, it would mean we had 3 times as much water within the planet.
Is that water going anywhere? Has it gone anywhere? No evidence whatsoever that has happened.