In playing Guild Wars 2 so far, I've only come across standard helms by way of the Trading Post. However, the filters also let you choose Aquatic Helms. When I first found this, there were none for my level. I figured it let you breath underwater for when I arrived at an underwater zone.
This doesn't exactly seem to be the case, as I can stay underwater seemingly indefinitely in the starter zone I'm in.
What is the benefit of an Aquatic Helm over a standard one?