This only works as long as u dont move. U can still turn arround though.
Just small 3 steps:
- Get in some water and swim at the water surface.
- Mount up a big mount. You'll notice ur mount will fall down a bit.
- Dismount and u'll be set beneath the water surface without breath time.
With a bigger mount u'll "fall" deeper in the water, so best use a mammoth.
I use this to hide myself underwater while afk kill mobs from this guide (The new way farming Motes+Greens+Skyshards!(Still requires Exalted with Golden Lotus)).