[dannypgh]

Most atoms- and certainly most hydrogen- are in stars, no? Not exactly places where water "breaking down at high temperatures" (really, never forming) can be ignored.

[jigg4joe]

Most hydrogen (and baryonic mass in the universe) is in the interstellar/intergalactic gas clouds

[raverbashing]

Yes, I guess not even H2 is much stable in stars.

I would expect that in planet formation situations

[saalweachter]

It looks like most stars are too hot for molecular hydrogen, but some stars have a bit -- our own sun has some molecular hydrogen in sunspots:

http://physicsworld.com/cws/article/news/2013/mar/13/cold-hy...