Continuity mistake: When David Mann is at the cafe, the waitress brings over his sandwich and water. He immediately drinks all of the water, yet when the shot changes to above the table, of him looking at his sandwich, the glass of water is completely full again.
Suggested correction: There is an empty glass next to the full glass.
The mistake is valid. David drank all his water before getting his food and asked the waitress for another glass of water and aspirin. She then brought him the food, aspirin, and 2nd glass of water. He drinks all the water after taking the aspirin and sets the empty glass down. In the next shot he's holding a glass with water. There should be two empty glasses.