Originally Posted by Brian Carlton

If the engine is not consuming the fluid and you don't see any external leaks, the odds are that the cap is faulty and is opening way too early. Then, the system discharges a bunch of water onto the pavement. You fill it up the next day after it cools and it does the same thing.

You could verify this, if you're interested, by putting the overflow hose in a small container and see if it fills during vehicle operation.