Choking on water

This is something we all have done, or at least so I think, I only seem to remember myself doing it. Its embarassing. What kind of signal does it send out when you are drinking clean, cold water, just like everyone else around you and you start to choke. Well, I finally got the insight to see what the answer to that question is.

The people around you begin to think: "What is wrong with you? You don't know how to drink water? How stupid are you! Freak!"

While you are choking you think: "Am I going to live? I don't know how to drink water! The other people around me make it look so easy! Why is it so hard to drink this stuff? Maybe I should just stop drinking."

My question is why IS it so hard to drink water? Why must I choke on this substance? And how do you stop yourself from choking and clear your throat? Normally when you choke on food, you can drink some water to clear your throat, but you can't clear water with water.