We house sat for 2 young mischievous cats a few months ago. It was the first time we’d come across the pet water fountains and have seen a few since then. 
The fountain these cats had was really good, except they were very naughty and kept pulling it apart. There was a little pump (the white object to the right of the fountain in the picture) attached to the fountain and it was stuck on the side of the bathroom cupboard with little suction cups.
The cats kept turning the pump over and then the fountain stopped working. On the last day we stayed there, they managed to get the lid off the fountain.
A few weeks later I went to look after a very old cat who is quite frail, but drinks a lot of water. 
Her owners said that one day they re-filled her bowl 6 times because she was drinking so much. The most important thing for them was to make sure it was silent because it was to be kept in their ensuite bathroom.
So they purchased a cat water fountain exactly like the picture on the left. Misty loved it and drank so much that one morning it was almost empty. It is very quiet – I didn’t hear it all night.
There are so many fountains and filters plus automatic feeders for pets nowadays, it must be difficult to choose one for your pet.