Well (haha water joke), not all of it is old. When you “burn” hydrogen, it combines with oxygen and “new” h2o is produced…
2h2 o2 = 2h2o (or liquid water)
Plants split h2o into h2 and o during photosynthesis.
It’s a fluid (haha water joke) system. Is it possible that we drink a little dinosaur urine? I don’t know (probably), but it’s not all ancient water.
There’s actually a way to date how old water is by measuring how much tritium (an unstable/radioactive isotope of hydrogen) it contains.
Just FYI, not trying to dampen (ha) the mood or be a wet (haha) blanket.