I have had a Drinkwell Pet Fountain for my two cats for about a year. This is one of the early models that had finally come down on price for me to try. It is not the most positive review. To be fair, the newer models may be different, I do not know. (Model number coming soon). I am just dropping a quick review in case you are thinking of getting one. I would insert a picture but the thing is in the trash and I am too irritated to drag it out.
Note: I am reviewing this based on its use for cats. Using this fountain for small dogs may be a little different as far as frequency of cleaning, etc. But it might still give you something to consider.
Random Bits of Projects 