How did Chris angel walk on water?

Um there was glass that went across the pool so it looked like he wasn't standing on anything but really he was... people could swim underneath him because there wasn't like glass from the top of the pool to the bottom, it was just like one thin layer on the top of the pool.... i don't understand why people think it was real... but I'm still trying to figure out how he could float from the roof of one building to another..