Kidneys.
It is not an organelle that is associated with osmoregulation but an organ system. That system is the urinary. The vacuole in cells, an organelle, stores water and may be what you are looking for.
The largest organ of a human is skin.
The male organ of copulation in humans is the penis.
The answer to that is skin.
organ
Plants,Animals and humans
Skin
Compared to what? It is the only respiratory organ in humans.
In humans the appendix is a vestigal organ and has no function that we are currently aware of.
It depends on the organ, animal species, and disease, but generally, with the diseased organ.
nose!
Plants,Animals and humans