水は綺麗。
(2010/4)
There's one at 258 Tran Hung Dao (next to Medicare) which I'm a member of and is quite a nice swimming pool. Its called 258 Club.
Its $2 for non members. Lots of lounge chairs, a good cafe/restaurant attached to the swimming pool. It can get noisy on weekends though.
258 Tran Hung Dao in District One, where entry will cost 80,000 VND and allow you to swim all day.