Water’s composition (two parts hydrogen to one part oxygen) was discovered by the London scientist Henry Cavendish (1731-1810) in about 1781. He reported his findings in terms of phlogiston (later the gas he made was proven to be hydrogen) and dephlogisticated air (later this was proven to be oxygen).
They have nostrils called blowholes. Over millions of years of evoloution whales and dolphins nostrils moved to the top of their head. This allows them to breath by surfacing instead of them sticking their whole head out of the water. The first thing a newborn dolphin must do is to go to the surface to breathe.