Ever been in the water and a creature fireball you and you take full damage, ridiculous huh?
Water is an "environment" like dolurrh is, it has effects on anyone who's in it.
Here's some things to think about.
1) time delayed drowning damage to all creatures that breath air after X time has gone by, overridden by airy water, water breathing spells or the non-breathing attribute of warforged. (already in game)
2) 75% fire reduction and then fire/50. So all fire damage is first three quarters removed, then 50 points is absorbed.
3) cold spells is slightly dissipated by water 25% Cold reduction. But theres 5% chance of ice entanglement. (like entangle spell, stops movement or slows for limited time)
4) Lightning /electrical area of effects is doubled in water. (shocking grasp becomes a mini shock sphere)
5) Acid is dissipated by water all durations for acid are reduced to 1/4 . Acid 50% reduction on all acid damage.
7) Physical missile fire is impossible when launched from inside water. For missiles launched from outside water damage is 75% absorbed.
8) Bludgeoning 50% reduction, slashing 75% reduction and DR 20/piercing (20 points from all non-piercing physical damage)
Water itself can be poisonous, extremely cold , corrosive, disease laden, negative energy charged or cursed, positive energy charged or blessed, thick and oily (slowing) . In addition to the above effects. (or replacing some)