I tried to kill some level 1 characters in the Water Dragon Cave and found that mist elven druids can safely walk to the Mother Dragon, look around, talk to her and leave.
It seems that characters that have max HP less than 10 take (practically) no drowning damage there, provided they know how to swim (typically mist elven characters have so low HP, and elementalists, druids, etc. with Swimming skill can do this).
If the max HP is greater than 10, he eventually drowns, if less than 10, he survives.

Moreover, animals are friendly to druids, so lv1 mist elven druids with low HP can visit that cave without any problems (only water elementals can attack them).