Bests & Worsts Reviews from Amazon

Ok, If you ask me, I would say just get the smaller one even if you have a big dog. I bought the big one thinking how awesome it would be to not have to change the water as often. WRONG! Even thought there is always clean water coming down from the tank, your dog will most likely soil the water in the bowl and therefore the clean water that comes down gets mixed with the dirty water already in the bowl part. My dog dropped a little drool, food crubs, and hair into the bowl part so the new water coming down mixed with the dirty water. I found myself carrying this to the sink to tilt it and emptying the dirty water so the new water wouldn't be contaminated. You're eventually going to empty the tank quicker by doing this and you will find yourself refilling this thing, so might as well get the smaller one since you're gonna refill it and empty the dirty water anyway. The big one can get kind of heavy as well so just giving my two cents...