Real Fall is a modification for Quake by Christopher Joseph, also known as Wrath. This modification attempt to implement realistic fall damage into Quake.
This is done by measuring the severity of the fall, which is reported on the screen for the player to see, as a number of feet. The amount of damage caused is based on the tens column, 10 or 15 feet will cause 10 damage, while 20 feet will cause 20 damage. Note that this makes drops that would normally not harm the player (20 feet) suddenly damaging, while drops that would injure the player before will now be a lot more severe.
On top of the mechanics above, Water will soften the blow, but if the Water is not deep enough the player will still be injured.