Maybe! Though Yasumi Matsuno the Wandering Dramaturge says that it's a gate to the Seventh Hell, while it is Mikoto that says Hell of Water.

What number IS the Hell of Water, anyway? Eorzeans seem like putting ice first and going clockwise for astral elements. We climb that order backwards when going from Hydaelyn into the heavens according to the Astrologians. Maybe Umbral / Hells associations are counter-clockwise inherently and we go "backwards" (the normal way) from the same starting point? Earth, Ice, Water, Wind Lightning, Wind, Fire? Hell of Water = Third Hell?

There was an old reference to Bomb Baron being from "The Sixth Hell" and that was the best I had for a theory as to why, lol.