So I couldn't find anything related to it and I don't think its common sense - so here some quick know how about the water walking mechanics:
Basicly it isn't random if you will smash onto the water or dive into, if you walk on water you will always dive in at a point where you look into with an angle of 45° or more.
So if you are falling look straight into the water up to a minimum angle of 45° an you will dive into it. If you look straight forward or with an angle less then 45° you will die.
I made a picture with my epic paint skills to make it more understandable:
Hope this helps to avoid (or cause) a few death.
/cheer