Pink slime in cats water bowl

How often do you clean your cats water bowl or drinking fountain? If you're anything like me you try to do it fairly often, but sometimes it doesn't get done as often as it should.  I mean really, am I supposed to clean it every day and refill it? 

cat drinking from freshly cleaned water fountain

For  years I would just add water to the bowl when it started to get empty. If it started to get funky or have floaters in it then I'd wash out the whole thing. But that wasn't very often until I learned about pink slime and the bacteria it contains.