Easy question

[strangefool]

It was a 104 degree (F), zero humidity day in Las Vegas. I was standing by the pool. Everybody that went swimming emerged from the pool and instantly began shivering from the cold. It was HOT outside...VERY hot, yet their teeth were rattling from the cold and the pool water was warm too.

Why does this happen?

I am a non-physicist being bugged by a mate about this. Need help to shut him up.

[zoobyshoe]

Evaporation causes refridgeration.

[Hurkyl]

My hunch is that most of the question is a red herring, and that the swimming pool is indoors and the thermostat is turned down low, thus chilling them as they exit the pool.

[kashmirekat]

If I remember correctly from Chemistry, what you're talking about would be classified as an exothermic reaction where heat is released. So when the water evaporates from the body, it is pulling heat away in an exothermic process, resulting in refridgeration as zoobyshoe said.