To find out how much your dog is really drinking, do what I did: Measure out the water into a measuring cup, then at the end of 12 hours see how much is left. If you aren't going to home, use a gallon bucket and fill it.
When I did this, I found out my dog was drinking 12 cups of water in that time period. WAY too much but I wouldn't have known had I not measured it.
She also did obsessive things like your dog, such as trying to lick rainwater from the leaves outside.