I have a counter top water filter. It's got two filters on it--one for chlorine, which is a carbon filter and the other for fluoride, which is activated alumina. It works, I guess. I don't know. As far as I know, you can't taste the fluoride and the testing strip showed no chlorine when I tested it, but then it also showed about the same in the tap water as well. (I am sensitive to the taste of chlorine, though, so I would know if I were drinking it.)
Anyway, I haven't changed the filters in a while. The chlorine one says every two years, and the fluoride one says every year. I was okay with the chlorine one, but the fluoride one...it's been too long. Okay, that's kind of embarrassing. Way too long.
I've had trouble with fluoride side before. Maybe I waited too long to change it previously--I don't know. But when I opened it up today...um, it had been too long. I wanted to throw the whole thing away. I called a friend and we talked about and it, I decided to clean it and just throw the rubber ring away and buy a new one. Oh and I threw out the old filters too, of course.
So I bleached and boraxed and when I get a new rubber ring, I'll put the new filters in and use it again. But ultimately, I think I will buy a new water filter.
And change the filters.
If you're interested, I got my filter from here. I don't think there's anything wrong with them; it's likely I just need to change my filters more often.