İ'm a teenager and I have a very simple question for my health: how many glasses of water should I drink during a day for a healthy body? :)

You should aim to drink 2 liters, which is about 8 glasses.

How big is the glass? If the glass is an 8 ounce glass, then 8 to 10 glasses per day. More water is not going to hurt you, while less water can lead to dehydration.

Well, lots of water will kill you (http://en.wikipedia.org/wiki/Water_intoxication). But by lots I mean LOTS