how should I polish water

[Invigor]

I'd try a canister filter with a micron filter in it. Worked very well for me, but the micron filter got plugged within a just few days. Does an awesome job if you don't mind cleaning it out once a week.

oh wait, just realized you don't want to add a canister filter...

hmm, I've heard good things about purigen. and it's rechargeable too!