Olympic pools are 50x25m, public pools here tend to be 25x12.50 or 16.6 (5 vs. 6-lane). And as I can actually swim, no, having to turn every three strokes is not an option. In a backyard-sized pool you don’t even get to swimming until after you turn: Start jump, dive, bonk your head on the other side before even surfacing.

Sure you can pace up and down an elevator cabin and call it exercise but don’t be surprised if runners are underwhelmed.

That said, having a pool with lanes is not at all necessary for exercise. Water park like situations tend to be superior if you’re not trying for lap times, I’d say.