As in GTA IV and SA, even if jumping from 1, 000, 000, 000, 000 meters won't hurt you if you get in contact with water.
Well I decided to change that with a small CLEO.
An amount of health will be taken from you after landing in the sea, which is equal to the distance between the water and you / 1.5.
CLEO is required.
Video
In The Guardian Ben Randall said that if you fall 5-6 fett you'll make it, if you fall 15-20 it's like hitting concrete, if you fall 25-30 feet, you'll die hope it's like that!