BUT it does eventually begin to make some noise, like any thing with a water pump. It's not terribly annoying to me since I keep it in the hallway where I only pass by every now and then. Can't hear it at all when doors are closed. Makes enough noise that some picky cats might be turned off but it's not a problem for my cat so it's definitely not a deal-breaker. I can sacrifice some hallway silence for clean, filtered water for my kitty.