It is from Earth, not from comets, not from asteroids.
There’s more than one million cups of water of it on our planet. Cups as large as the comet was 65 or 66 million years ago. There wasn’t enough time for all our water to be delivered this way. Where in time are you going to put all those alleged events?
None of the latter big bombardment were nearly big enough.
Almost all of our water for the last 4.5 billion years has always been with us. Just as all the sulphur has.
Chemically recombined who knows how, but all the water is originally from here.
(I won a bet on the Extropy mailing list, what Rosetta was about to say, a few days ago. It is in a perfect accordance with what I have written above.)