By the way, preliminary calculations show that the 3 foot dia. hole app. 7600 miles deep would contain roughly 381,000,000 cubic feet of water. I think.
Anyway, how many cubic feet of water are on the planet? What percentage would 381 million equal?
There is about 326 million cubic miles of water on Earth, so your 381 cubic feet is only 0.00000000126% of the total. Assuming minimal density change, of course.