Guild Wars 2

It doesn’t work. Since your helm is replaced by the breather(?).

It does, however, work if you go to the surface of the water, but not below. And once it has activated at the surface, it doesn’t get deactivated when you go above the surface of the water. Effectively giving you 100 extra power above water, instead of under it.

To get the 6th bonus underwater you need to put another rune on the breather.

Yep, but that does seem somewhat kitten . And as previously stated, it bugs when getting out of the water :P Giving you the bonus permanently when above water.