Briefly, the film is (and I'm not giving anything away here, don't worry) about a young woman that visits her mother in Thailand where she runs a quiet vacation resort. Also living there is a caretaker, a young Thai boy and an older woman. They talk a bit. There's a pool. And... that's it, really.
If this sounds suspiciously similar in style to both Megane1 and Kamome Shokudo2 then you're quite correct. The overall mood and pacing is very similar. People meet, nothing much happens, it ends. Sounds pointless, I know, but you sit and enjoy it all the same. Is "Pool" worth seeing? Yes, I think so. It's better than Megane, which had a preachy undertone; but not quite up to the level of Kamome Shokudo, with its whimsical sense of the absurd that makes it one of my favourite recent films. "Pool" is a solid, fun movie well worth seeing if you have the chance.
#1 Woman comes to southern Japanese island for vacation, meets odd people wearing glasses.
#2 Japanese woman has a cafe in Helsinki, befriends odd people, makes cinnamon rolls and onigiri.