Ever since I got my first two fish, i've been filling the tank with filtered water from my Pur pitcher. I live in a dorm, and I don't drink the tap water so I didn't see the point in making my fish live in it. Is this ok? My oldest fish is 7 mos and my newest may be around the same age since their about the same size, but the new one is a common and the oldest is a comet. They seem to be fine with it, but I want to make sure. I'm getting them a brand new tank in a few weeks, 20 gallons, and I'm trying to gather information for when I move them.

Dunno. What does it do to the water?

Could you test pH, GH, and KH in the filtered water?
If you don't have the testers, you could take some filtered water to your local pet store and they'd test it for you. Have them tell you specific numbers rather than Oh it's fine.