I give you: Five noteable swimming pool scenes, in no particular order.
A Man Called God
Boys over FlowersThere's tons of swimming pool scenes in this drama. Well, of course, since the lead lady plays a talented swimmer. When I went back to this drama to do some gifs, I couldn't believe I ever watched and liked it; the acting! the characters! everything! TERRIBLE!!! But I'm degressing. I decided to go for two out of the many swimming pool scenes. No 1: when Lee Min-ho falls into the pool early one and 2) when he plays a prank on her. The ducks are great. Though clearly 'photoshopped' in. Or whatever the equivalent is for film. I'd say that the swimming pool is used solely as a plot device in this drama. She agress to go to Shinhwa High cause of their state-of-the-art swimming pool. Jun Pyo cannot swim - she can (until she gets her shoulder insured because of him). But then, he learns how to swim for her. And when he gets amnesia (duh), she falls in the swimming pool so that Jun Pyo can remember (duh). Etc.
Vampire Prosecutor 2
Finally, there is one classic use of the swimming pool in KDrama: The swimming pool as a site for murder. This is used in both seasons of Vampire Prosecutors. In season 2 (gif), it's for a movie. A vampire movie. A vampire movie within a vampire drama. In season 1 (still), it's also about a film production, but the murder is real, not fake.