Waterbirth is certainly the calmest, most gentle way to bring a baby into the world. Some call it the "natural epidural" for Mom, and it eases a baby from the watery world within, to a watery world on the outside to meet mom earthside for the first time skin to skin. Babies have an amazing natural swimming reflex when they are born - likely carried over from swimming within for so many months. And no, they do not breath underwater and drown as they have been living in their watery world and "breathing" amniotic fluid for all this time. Their first breath of air comes when their body enters the non-watery (air filled) atmosphere. As long as their body stays within the water until their head emerges, all in waterbirth is wonderful.
Below is footage of the waterbirth of twins! Peacefully, gently, beautifully filmed.