Indiana Jones and the Last Crusade - Truly Holy Grail
When Indian gets the Grail and returns to his father, he pours the complete cup of water on his father's wound. But about 10 seconds later the cup is almost full again. Ha. Look for yourself.
Actually it does refill itself. If you know some of the myths of the Grail (stuff that is added to the legend long after the legend happened through movies and t.v mostly), one of the myths is that the Grail cannot be emptied. It is always full.