I change out the filter every three months. But I’m at six months now with the pitcher.
I keep the thing in the fridge all the time, except when pouring water or filling the reservoir.
So basically the entire usage of the pitcher is this: Fridge -> remove to pour a glass of water -> refill reservoir -> back into fridge. Whole process is no more than two minutes.
I don’t notice any funny smells or see any scumming or growth. And the water still tastes great.
I wash it when I change the filter (8 weeks + procrastination). I keep it in the kitchen, where it develops a film of oil from cooking (hood doesn’t work).
About every 3-5 months. I disassemble the entire thing and go over it good with a green scrubbing pad with Dawn to remove any calcium deposits and stuff like that, then a very thorough rinse before it gets put back together and refilled.