It's possible, of course, to set up something like this, and we have several existence proofs that it can be done (e.g., Hukif's gravity ADA/RC), but to be effective it shouldn't IMO be something so specialized as being underwater, unless you dream of being underwater a lot already. It should be something always with you: your breathing, the feeling of gravity, your location in general, and so forth.

It also seems a bit like the incubation approach: establish frequent visualization of a particular scene/situation, recognizing it as a dream, and then incubate that situation by thinking about it all the time. I had some luck with that when I was dreaming a lot about my childhood home (almost every night), but I think you need to be pretty good already at incubation in order for that to work.