I turns out, when you put TNT on soul sand even after watering it up its gonna explode and break everything.
When TNT is exploded underwater it doesn't do block damage but when it explodes IN a block it breaks everything. So because of soul sand's collision hitbox which is not a full block, the TNT blocks position gets counted as INSIDE of a block and even water cant help! This is a great feature i noticed and i hope it can be used in some traps or cannons!