Erdolliel settles into the water and sinks down a bit. The water isn't too cold, though it is incredibly salty. The elf swims down a bit, but realizes in short order that the light from above does not afford her much ability to see, and it is soon pitch black. With help from the others, she easily makes it back up to the half-barrel, breaking the surface and gasping for fresh air.
Erdolliel doesn't know how far down the shaft goes, but it is certainly beyond a few feet.