I wouldn't submerge first unless you cant tell from these:
Goto a quiet room, put it close to your ear and hear it. common spot 3 spots Fill Valve, Release valve, and the gas release spot.
If you can't hear it, spray a lil LIGHT silicon oil, (helps lube it anyways) listen for bubbles
If those two doesnt work, well then chances are its good, or having a really really slow leak.
Down side, if you listen to loud music..like those people blaring music even though theyre wearing earphones...it might be difficult for you as you killed yourself. hehe.