Great inks indeed! The concept is very old and seen in popular films and books as well. Remember the scene in Lord of the Rings, where Frodo or Sam is dragged underwater in a bog. I guess it has to do with the deep fear of the dark depths of the water and the unknown & unseen terrors that lurk there. Fear of the dark and fear of the deep must be the most primal fears for humanity! You also seem fascinated by the depths, I think I remember another drawing with a witch going deeper and deeper in the water with her huge hair flowing all around.