The act of receiving head while in a bathtub/pool/hottub/ocean/etc.
You might wanna clean your pool cause your mom gave me aquahead in it last night and i came all over your shallow end.
To recieve oral sex while in a submersible. See Roadhead
"As we reached our final destination at 20,000 leagues, my supermodel colleague thought it was only appropriate to engage in aquahead."