This is a wonderful piece of work. It is nicely composed, and there is great atmosphere.
There are a couple things that stand out, however. The first is the lighting on the model. She seems overly bright for the darker background. Also, given the direction the light is coming from, she should be flipped (the light is in the upper left, yet she is brightest on the right). Her skin should also have a bluish cast to match the overall tone of the picture.
Another thing I see is the brightness of the water; it also is rather bright in comparison to the rest of the manip. However, this may not be a bad thing. If you actually give it more highlights, it could appear to be glowing. That would simply add more magic to this awesome work.
You have done a magnificent job with the blending. The background and model fit with the water perfectly. The placement of the water splashes is great. Even your watermark fits the piece.
I hope this critique helps you in some way. This is certainly a stunning piece, and you should give yourself a pat on the back for the hard work.