Poor kid -- I would think people with pools and small children would take special precautions, but it is impossible to know.
Prayers for the kid an the family.
All the precautions in the world won't replace parental supervision.
Here is Phoenix, pool fences are required for all new homes. Even with fences, curious children find ways to sneak in.
There have even been child drownings when mulitple adults were home at the time. Everyone just assumed that someone else was watching the kid.
It happens on a weekly basis here in the summer. It's tragic.
There is no better precaution that parental supervision.