What about beyond that? Most of our bodies are hydrogen, carbon and oxygen, but nitrogen, sulfur and phosphorous make appearances too...so does other stuff but it tends to be stuff like iron or sodium that's only used in a few molecules in a few applications and we don't possess that much of it.
You kind of wonder if civilization could ever get off the ground in a water nebula, though... for all we know, dolphins may have language or something not unlike it, so the most basic thing that really makes us that different from other smart animals is fire. You might be able to get agriculture (kelpaculture?) started in a water nebula, but metalworking ain't gonna happen.
It does make me wonder what you could find in a water nebula that would allow you to have sentient species at all, really. If it's galaxy-sized, it's not inconceivable that it would contain planets and things it had swallowed up, but could it have stable solar systems in it? I doubt it. Again, energy will be a big problem. Unless you could somehow have bubbles of vacuum that had solar systems in them (how that would work I don't even know.) Then you'd have two different sorts of biosphere: normal ones on normal planets and a bigger, more nebulous, far less diverse one in the cosmic ocean that had been seeded by comets and things that had wandered too far, and with...like...chemosynthetic organisms that fed off the rock with help from the light of distant stars.
On the other hand, once you've got space exploration and a method of propelling your spaceships with fusion, you're golden, because you can never run out of fuel...