I never really watch swimming until the Olympics roll around, but I had never noticed that before they dive in, the swimmers drink the water. After my crowd of friends pondered the reason why - we remembered that the internet existed and decided to put an end to the speculation.
According to wiki.Answers:
This is to prevent the gag reflex that can occur from accidentally swallowing water while swimming. By tasting the water in advance, the mouth is made accustomed to the taste and quality of the water and its additives.
Well, thanks to Gold Medal winner Ryan Lochte, we now know what one additive is.
In an interview with Ryan Seacrest, he was asked, "Do Any Of The Athletes Pee In The Pool?"
Of course. I think there's just something about getting into chlorine water that you just automatically go. [I didn't] during the races, but I sure did in warm-up.
That's right folks. All Olympic swimmers ritualistically ingest a mixture of piss and chlorine to get themselves going.
Gag if you want, but I know a hand full of you just got a craving for pool water.