Vanish hardly drinks any water during the day. We are mixing her food with more water so that we know that she is at least getting some liquid. Is this typical behavior?

Opie never seems to drink more than a few laps in a day. Even if we're out on a hot day he won't drink until we get home. My others definitely drink more than he does. We put water on his food also. If she seems healthy otherwise, I wouldn't worry.