Like Riddles?

Try this one for size:

You are in an empty room and you have a transparent glass of water. The glass is a right cylinder, and it looks like it's half full, but you're not sure. How can you accurately figure out whether the glass is half full, more than half full, or less than half full? You have no rulers or writing utensils.

Apparently this one is classified as an "easy". Hope you can solve it. You can find hundreds more at this riddle site.

If you really cannot work out the answer, you can find it here. (via del.icio.us)