Open Water - supposedly based on a true story, but as the two divers were never found, how do they actually know how they did die, which is what the film dwells on most.
If your a novice scuba diver you'll never want to get on a dive boat, and if you've never dived it might make you unecessarily worried.
If your an experienced UK scuba diver it makes a good comedy. There's so many things done wrong by the divers, and they've not got basic safety kit with them, as well as the bods running the dive boat. I get the impression that however directed it has only just about got wet in a swimming pool.