Breathe the Waters of his Glory?

Alright what am I missing here? I assume I have to use the water in the center of the puzzle canal but I can't figure it out. First I tried using Water breathing and it didn't work.

Next I tried to drown myself until around half HP, you know... something i think would be reasonable in desperate confusion without coming across like an idiot with a deathwish. It also doesn't work.

I just don't get it.