Basically the same thing as when you fill a non-stick pan with water. Hydrophobic coatings only repel water in a way so that it doesn't stick to the surface. That's why they use hydrophobic coatings on windshields, so the droplets of water slide easily and quickly.
Granted, the effect is more noticeable with hydrophobic coating than with non-stick coating, but if you were expecting the water to visibly float away from the walls, that won't happen with either. Reality is sometimes disappointing, huh?