Interestingly, I remember reading many years back a bit saying that water is believed to be the 2nd most abundant molecule in the Universe after the hydrogen molecule, and has been observationally found of course in every cool enough body in our solar system, in clouds of interstellar matter in abundance , and also in many various exoplanets observations. This has to do with how oxygen is one of the the most abundant heavier than helium products of supernovae. Let me see if I can find a nice article to lay out some about it.
Ah, I see that if you count an H3 as being another molecule (H2 being the most common molecule), then water would not be 2nd (and some views about other common molecules like HO and CO, etc. could put it down a little more), but it's super abundant. This is because oxygen is more abundant than carbon. I'll grab a reference or 2.
According to Chandra's data, the exploding star blasted off 10,000 Earth masses of sulphur; 20,000 Earth masses of silicon; 70,000 Earth masses of iron; and 1 million Earth masses of oxygen...
We Finally Know What Elements Are Contained in an Exploded Supernova
Relative elemental abundance in the Universe is thought to be:
1 Hydrogen 739,000
2 Helium 240,000
8 Oxygen 10,400
6 Carbon 4,600
10 Neon 1,340
Abundance of the chemical elements - Wikipedia
So, basically, expect to find at least some water in
every planet except possibly (my speculation) some that are hot enough by being close enough to stars or with sufficient stellar wind in combination with radiation to have dissociated it and evaporated away the hydrogen (as Mars has experienced we think a lot of for example, but we find water on Mars simply underground and/or at the poles as ices, etc., as the planet is cool enough). Note that often the water would be vapor or ice, not liquid, but it's going to be everywhere cool enough in some form, pretty much.
But, it will still be news that many would like to hear, no doubt, that we found water in exoplanets (even though yet again as so many times already) in more observations today and soon.
I'd just like people to become aware it's in most every planet. (actually, to me, not finding it in a planet is more interesting than finding it because not finding any traces or only a tiny trace requires an explanation, and those are interesting explanations in themselves)
When we find methane, etc., organic compounds in explanets -- common molecules produced abiotically, and even including O2(!) -- I've...gotta feeling we are going to have to explain more than once or twice these don't require life or demonstrate life, but more evidence would be needed. I'd be delighted if we can find more convincing evidence than methane or molecular oxygen (which don't strongly indicate life) that a planet might have elementary life (like something akin to algae or whatever) --
that would be something.