"Both sawyer and first need make filters that filter viruses."

Sawyer already does:
http://www.sawyer.com/sawyersaves/products-pointtwo.html

Yes, that is what he said... BOTH SAWYER and FIRST NEED make filters that filter viruses,and indeed they do.

You should never trust a frozen filter if it uses hollow fiber technology like the Sawyer, Platypus or MSR HyperWorks, etc. If the tube is ruptured it no longer stops the baddies.

The Katadyn Hiker uses a paper filter element that is the best in sub-freezing temps. Many trips I have used one to filter melted snow (rather than bring it to a boil) for Dave and I. I pump it clear of water and keep it in a ZipLok in my bag at night, and just buried between my sleeping bag and extra clothes in the pack during the day.

Ha! My brain added the word "to"..."...and first need to make filters that". My bad. :O)

Again, thank you for all the info

Does anyone have a reference showing that untreated melted snow can be hazardous? Surely not as it fell from the sky, so the issue must be what happens after it lands. Naturally we are talking about clean white snow in the wilderness -- not snow with visible dirt, and not snow where there are many people.

It might be okay if it's freshly fallen, but after that it's unreliable.

Believe me, I ski and walk around lots of snow, old snow, new snow, dirty snow, clean snow, and especially pink snow. I avoid yellow snow.

Clean snow seldom has any problem at all. As a result, in the winter time we melt it, but not boil it, before we consume it. Once you put a layer of muddy animal tracks across it, it might have a problem. However, we generally just scrape the top couple of inches off and then grab the clean-looking snow underneath. Sure, there could be all sorts of problems with it, but we've never found any.

In the summer, you might find pink snow, and there is a problem with it. Pink snow is actually an algae that grows on the boundary between barely melted summer snow and pine pollen. It is pink in color, and sometimes it has a faint smell of watermelons. So, sometimes it is called watermelon snow. When in melted snow, it is not lethal, but it can cause diarrhea, and that isn't good.

--B.G.--

Not much grows at freezing temps.

It grows much better once it's in your warm belly. The cold is good for the survival of micro-bugs. Even things like chlorine and iodine take longer to sterilize at cold temperatures.

"You Must Sleep with it if near freezing weather is to occur (freezing will damage the filter)"

Are you sure? I read that on the REI web page and a google search turns up lots of references saying that, but I didn't find it anywhere in the documentation that came with mine or on the Sawyer web site.

The only mention of freezing that I saw from Sawyer was that freezing full bags could damage them. I have to wonder if maybe that started a possibly false concern over damaging the filter. I can see where freezing it might crack the body if it was not shaken out, but wonder if the concerns for the hollow fibers are valid.

Anyone have info on this from the manufacturer that I have missed?

"Anyone have info on this from the manufacturer that I have missed?"

From:
http://www.sawyer.com/waterFAQ.html

Q. Can the filter be frozen?
A. While we have no proof that freezing damages the filters we have no proof that it does not. Therefore we must recommend replacing the filter if you suspect it has been frozen.

Q: Can I dry my filter out and then store it in freezing temperatures?
A: No, it is almost impossible to get all the moisture out of a filter once it has had water in it; and the small amount that remains will/may cause damage.

Q. How do I use the filter in freezing temperatures?
A. You will need to keep the filter warm when not in use. You can carry it in an inside pocket close to your body and use your body heat to keep it from freezing. At night bring it in your sleeping bag with you.