Considering the fact that you're 13 years old, this is very great work! I can see you've challenged yourself in trying a new medium, and attempting new styles, like not using linework, and these are very positive things to keep doing to progress. Try new things and methods and you'll learn a lot, very quickly. A few thingsa you could keep in mind, water is a VERY tricky thing to paint, I have trouble with it every time I attempt it, in this picture your water looks a little like smoke vapor. Try making the edge of the water, where it comes into contact with objects, a little more solid and wrapped around the subject. Also make the object itself, in this case the girl, less visible when in the water, and even try distorting the parts visible underwater (with something like the liquify tool). Great work, keep it up, and thanks for sharing!