|"A Bigger Splash," David Hockney, 1967|
The Banneker Pool at Georgia and Euclid, the nearest one to most of Columbia Heights is open 8am-9:30am for lap swim, then 1pm-8pm for general use every weekday except Thursday, when the pool is closed. On weekends, it's open noon to 6pm.
As for other nearby pools, the Upshur Pool at 4300 Arkansas (near 14th and Upshur) is open the same times, but without the lap swim portion, and is closed every Monday. The Harry Thomas Pool (that's Senior, not his son the crook) at 1743 Lincoln Rd
Personally I am a big fan of the Banneker Pool, which is free if you have a DC driver's license or other official DC-issued ID. You have to get there early though. I know others have had issues with it, but I've always had a blast.