How often to change water in those water bottle dispenser bowls?

Ok I'm not sure if I described that right Reeses has one of those water dishes where where you put a 1 or 2 liter bottle of water in and it refills as necessary.

How often should these be changed, especially if the cat doesn't drink much? I made the newbie mistake of filling a 2 liter bottle all the way thinking she'd drink it over a few days. She did a bit, but over the last day or so it doesn't look like she's been touching it. Then this morning I found her in the shower, which my wife thinks may be because the water isn't so fresh any more. (of course she's in heat and in the morning drives me nuts and gets into everything anyway..but she's cute so you let it go)

So I changed it and only filled the bottle maybe half of the way so she'd atleast run out quicker and then I'd have to refill it. But how often should I change it even if it's not totally empty?

Good question. I change the water in most of the water bowls every day, while leaving one bowl to be filled every other day, as Jamie seems to enjoy "slightly stagnant" water at times. The drinking fountain (Fresh Flow, with a filter) is cleaned and refilled once or twice a week. I'd tend towards thoroughly rinsing the bottle and refilling it every day.

I have one of those and it really depends on your cats. My girls end up with a lot of food in their bowl so I change it when I see food floating in there and rinse and scrub it good an refil with fresh water. But They have run completely out in the bottle before i have changed it before and had no problems.

I feed them in one room and have the PetMate fountain in another (so there is no food floating in the water). I clean the PetMate thoroughly (take it apart) and put in fresh water every Saturday.