*Adults take a while to drown. They thrash about, yell, struggle. Almost all adult swimmers who drown are out of their depth.
It takes them longer than it takes chikldren.*
THIS... is not true. This is SO so dangerous.
Adults can drown VERY quickly, their only advantage over children is larger lung capacity, but they can still drown in around 40seconds.
Adults do not splash, shout or struggle, just like kids, they slip under the water quietly and gone...
As for 'life guards are on the side' - yes, but they're usually sat up high looking down on the pool (and if they aren't, they should be). Giving them a much better view of the pool as a whole.
If you're supervising ONE person rather than a whole pool, you need to be IN the pool with that person.
A kid can drown in 20 seconds. Can you honestly swear that you can spot NOT 'your kid yelling and splashing' because they're ALL doing that.. but your kid NOT there NOT splashing NOT yelling.
Because that is what you're looking for.. not activity and noise, you're looking for the LACK of activity and noise. You're looking for something NOT there.
In a busy noisey pool it is VERY difficult to spot something missing.