Hey, I'm the guy who created the crazy elaborate setup for filtering the vodka. So to answer the "why" as opposed to the "how" -
And finally, if I'm going out to a party, of course I'm buying a nice bottle of vodka. Home with the guys? Filter all the way.
Further notes -
Also, aside from the silver-impregnated carbon, the Brita filter uses ion-exchange resins (the little white beads mixed in with the black charcoal beads). Their particular ion-exchange resins are crosslinked polystyrene, and again, this material receives the highest rating of chemical resistance to alcohol. So no problems there, again.
Sure, there may potentially be some very very very slight risks involved...but isn't that what drinking is all about anyway? And everything I can find on the subject points to this method being as safe as not filtering at all.
Considering the choice is to drink unfiltered vodka that knowingly contains many nasty contaminants, versus drinking filtered vodka that may potentially possibly maybe have a slight amount of conaminants...well I'll go with the latter.
1) PVC (not just CPVC) is rated as safe to use with alcohol.
The only difference between a Brita filter and a regular filter is a Brita filter is typically impregnated with silver. But, many alcohol corporations use silver-impregnated charcoal for their filtering as well.
We're just doing the same thing the companies do on a smaller scale.
Oh, one other thing -
My friend and I both experience almost NO hangover effect at all from the filtered vodka. We'll get pretty damn drunk on the stuff, but the next day there is no hangover at all. That in itself makes it all worth it, for me.
Going through the comments, I see a whole lot of speculation and hearsay, and no actual evidence. So here are some comments from someone who has not only tried it, but gone fairly excessive with it.
1) Will you taste a difference? Absolutely, emphatically yes. After just a single run through a fairly new brita filter, you will notice a big improvement. After 3-5 filterings, you will notice a substantial difference.
2) Will it taste like a top notch vodka? No. It will not *taste* like a top notch vodka. But it *will* be as smooth as a top notch vodka.
3) Who can tell the difference? A top notch vodka connoisseur will be able to tell the difference, a la the Mythbusters episode. Will your friends tell a difference? No way.
4) Will it ruin the filter? No. It will not. Period. Granted, every filter has some sort of shelf life and will stop being effective eventually. Maybe the vodka speeds this process up some. But, once a weekend I would triple-filter my vodka through my regular water brita filter, then run water through it 3 times after, and my filter didn't taste like vodka, and still remained completely effective at smoothing the vodka out after several months of doing this once per weekend. (Yeah, my liver hates me.)
Another way to put it - after filtering vodka about 50 times through the same filter, I could tell no difference in quality between the first filter and the last. Just remember to flush with water from time to time.
5) Can I get extreme with this? Hell yeah! My friend and I spent a Saturday building a filter-kit specifically for vodka. We built the device (pictured below, hopefully) using simple off the shelf components from Home Depot and a 10 pack of brita filters from CostCo.
Basically, "the device" consists of 5 brita filters, each trapped in a PVC coupler, each coupler separated by a 5" piece of PVC. The long tube on top is to contain the bottle of vodka. The vodka goes in the top, enters filter one, drips to filter 2, and so on. The whole setup cost about $80, though we still have 5 brita filters unused, so really the cost is $65ish? And we've already gone through about 6 bottles of cheap cheap vodka. With an average savings between $10-30 per bottle of vodka (if we went with the good stuff), the device has already paid for itself. "The device" is easier to use than putting charcoal in a bottle and shaking once a day for a week and easier than using just one brita filter over and over and over.
And yes, the end product is extremely smooth. To the point where you can drink the vodka straight like it was a glass of water.
We plan on putting up DIY plans for building the vodka filter system soon.