
Continuity mistake: When Lucius is putting aftershave on in front of the mirror, he hears the robot outside and runs to the window, leaving the bottle of aftershave on the desk with the lid off. He returns to open the drawer, and the lid is back on. (01:29:00)
Chosen answer: If any object can move across the water quickly enough, the weight isn't transferred completely. In some Scandinavian countries, they actually DRIVE very quickly across water in adapted vehicles. If the character of Dash could actually run that fast, it is feasible and possible for him to run on the water's surface.
GalahadFairlight