I have looked everywhere and have never seemed to find the answer to this problem. I'm running Fallout New Vegas with everything completely maxed out and when I go near water, either I see right through it, it has no impact data, it acts as if it's regular terrain (if I shoot into the water, it hits the bottom and makes a regular impact, same with explosions), my characters hair will disappear under the water, or I can actually see the normal maps when I'm under water.
I don't know if this sounds crazy, but this has happened to me on multiple installs of the game.