DiveMaven hit the nail on the head Open Water is 'based on a true story', but the only true bit is that they were left by the boat. The rest is all creative bollox as no one knows what really happened.
The only thing that is funny when watching this crap is to see the woman's reaction to the sharks. I interviewed both the main leads (if you can call them that, they were out-acted by the sharks, in my opinion) and she was terrified of the sharks, so when you see the two of them on the surface and the sharks surfacing near them, she does look extremely scared. However, then look at the scenes when she is supposed to be splashing the water to scare the sharks away (these scenes were shot in a completely different part of the Bahamas where there were no sharks, obviously, they didn't want the actors thrashing about near the real sharks, as even though they were only Caribbean reef sharks, they could still have got agitated and had a nip) and look at her expressions. She is having to 'act' scared and it just doesn't cut it. The guy, on the other hand, loved being in the water with the sharks. And would you believe it, the only marine injury was caused during the filming of the recreational diving at the beginning a barracuda took a nip at her hand for some reason, probably going for her jewellery or something.
Mark