Well, the fact you're just switching between PT and standard is the issue. You also have to deal with lighting issues in shadows where noise will show. Higher quality settings.
PT water needs more customized density settings. Which is why the depth looks less intense in PT, because the default effect is lessened from stanadard.
I do notice the shadows look terrible still. There is no transmission, which to me is a bug and wrong, as PT should most certainly be offering this.