Aquan grew from a proto-elemental language which was the progenitor of all elemental languages. Much of its vocabulary is taken up with water-related terms. It is a guttural language with many long syllables made up of dense, throaty sounds . As a result, place names like Bue'kaa and Kol'taa are approximations of Aquan words that only sound true when spoken underwater.
As would be expected, Aquan carries well under water but requires practice and study to understand the language on both land and underwater. The elderaunts, one of the few land races that have this as their native tongue, typically only understand the land version of the language. They may only understand 10-20% of what is said underwater, unless practiced in it. Deep Bred spend a lot of time in the water, so they are versed in both the land and underwater usage.