I'm saying the water may have come from the seamen's quarters as well, but I'm not sure of it.
The flooding may have been chaotic, but chaotic doesn't mean destructive. At the earlier stages of the sinking, the water moved slowly enough to flood rooms without doing any erosive damage. Just look at the damage of the Grand Staircase: A Deck to C Deck are badly damaged due to the water rushing in from the broken sky dome, but D Deck and below were already flooded and thus much better preserved.