I think water could be improved, here are my suggestions:
1) Submerging under wate
When in water, if you crouch, you can go under and sneak around in the water undetected. You can resurface by releasing the crouch button. And to not make this OP:
2) Oxygen Bar
When you are underwater, you have an oxygen bar that will deplete slowly whilst you are underwater. If it runs out, you die.
Your oxygen bar will refil itself when you are above the waters surface.
3) Player bobs up and down on surface of water slightly when still, and more when moving.
>Discuss.