Our rule is no one, including adults, swims alone. My wife is in the medical field and is concerned that an adult swimming alone can have some kind of medical event(stroke, heart attack, seizure, etc) and will end up quickly drowning. Having that same medical event outside of the pool can result in a much different outcome. However, this doen't prevent me from floating around in a raft since I consider this to be out of the water. :-D