Corinnguard
Hero
In 5e and earlier editions of D&D, Sea Elves were able to breathe both air and water. For A5e, my take on the Sea Elves has them being air-breathers who live in floating 'ship towns' that travel the seas. They can hold their breath for a period of time.How "aquatic" are Sea Elves anyway? Are they amphibious and can live in air and under water?
As a culture there might be some sort of ritual that may change their ability to hold their breath for a while to full water breathing.
Or if water breathing is a heritage gift, a Paragon gift may be to grant someone the effect of the water breathing spell.
That's what I like with A5E... there are so many options where you may vary things and none of it has to be "wrong"