Hmmm...a water filter, huh? I'll have to dig around for this, 'cos this is a GREAT idea.
I have the same problem, and couldn't figure a decent way to vent the fumes.
Here are a couple of articles I came across:
http://www.iams.org/iamsorg/p2iris/painting/3684-w.htm
I just shot Ric Golding an e-mail (go to the source!)...I'll post if I get a response.