When I was a guard in AZ, we safety drills infrequently (maybe once a week or even less). But a drill was a full-on re-enactment of an actual emergency. One of the guards would put on a t-shirt or white swim cap and try to find a spot that wasn't being guarded as carefully (such as right under the guard chair, or behind it). Or they would wait until a guard was preoccupied with talking to a couple of unruly kids. Then, as soon as one of the guards saw the "victim" they would blow the whistles and everyone would leap into action just as if it were a real emergency. This served several purposes:
1. Keeping the guards on their toes at all times
2. Helping keep the emergency procedures fresh in all the staff minds at all times, like how to get a spinal injury victim out of the water safely
3. Helping the regular pool patrons know what to do in an emergency and to keep calm
We sometimes did a drill if the pool was very very crowded or the kids were very feisty that day, just to calm things down. Inevitably when we did the drill, some people would leave.