The Pool (2001)

To celebrate the end of the semester at the Intenatinal High School of Prague, Gregor organizes a party for his friends in a secret location.  The uber exclusive party turns out to be at a huge indoor pool in a fancy building.  The pool has covered slides and a bar area filled with alcohol.

Our lead girl who is Gregor's girlfriend, is not happy as she is deathly afraid of water.  As the others splash around, she hangs out nearby at the bar.  Soon people are splitting up to go off by themselves, which makes them easy prey for the masked killer lurking within the building.

Once the first murders are discovered, the group tries to leave but find they are locked in.  As they try to find a way to escape the building, people keep getting picked off and the killer seems to know their every move.  How can it be?  Could he be one of them? Will we even care? Oh the humanity!