Endoscopy is in the afternoon and i can drink water after 12am why ?

To avoid thirst: If your procedure were in the morning instead, your doctor would have recommended that you have nothing after midnight, including water. Because it is so late in the day, he is allowing you to have some water, in order to keep you from feeling too thirsty. I would recommend that you have a small amount when you wake up in the morning, but be sure to avoid any solid food until after the endoscopy.

Because liquids...: Because clear liquids leave the stomach much faster than solids. You must have empty stomach to prevent vomiting and aspiration due to the anesthesia. Most anesthesiologists allow to drink small volumes of clear liquids up to 2 hours before anesthesia. However, do follow what you were told by the endoscopy facility.