In the comics, the Flash can vibrate his body so fast that he can walk through walls. With water, though, vibration can keep water droplets from being absorbed into a larger surface of water. Instead of coalescing into the larger body, they just gather on top as long as the surface is kept vibrating. It’s amazing to see, and when you stop to think about what you’re looking at, it doesn’t seem to make an ounce of sense — except obviously it does.
Science! [YouTube]