Actually, the water does cool you down - not immediately, but 3x faster than normal and even while you are shooting. Its in one of the voice-overs, but as you said - they easily get scrambled into one another.
Or even better some evaporating water around you. I think what confused me was that the heat bar still moved and the heat icon also popped up. I expected to have no heat effect at all while in water. But this is all something a little polishing can make clearer I think.
