The realism in this is impeccable... I've neither attempted nor fathomed such a vivid piece depicting something underwater - a person, no less. Even though this was taken from a photo, it seems as if you have a solid understanding of lighting and depth.
I took a look at the website, and those are some beautiful art references; it's no wonder your piece came out so well. Having looked at the photo from which you derived this piece, however, I have a few criticisms:
Altogether, this seems very, very accurate, so it wasn't until I looked at your reference that I spotted almost any difference. The front of the neck and eyes of the figure where what appeared patently different upon comparison (namely that they appear to jut forward a bit in comparison to the stock photo); also, the mouth is a bit larger than that in the photo - something I noticed almost immediately; additionally, the hair is a lot darker than that of the photo - not to mention less voluminous - which makes quite a difference. In general, the piece has much more contrast in comparison to your piece. And, although I really don't want to try and criticize this (because it's obscenely beautiful), the water droplets at the top are a tad large in comparison (again, it's still obscenely beautiful); I also understand that making them that small would prove difficult in terms of adding detail to them. In brief - and I'm not to sound disparaging in any way: lighten it up, add contrast, and pay a little more attention to the stock photo.
Again, just to clarify, I think that this piece is amazing. Also, my criticisms were in no way a form of derision or contempt, but a form of constructive feedback; I hope you benefit from them in some way.