I wouldn't use without chemicals unless the mfr provides more info. It may filter out giardia and crypto but there is no indication of how fine the pores are so no guarantee it will filter out smaller bacteria.

And it will only filter 50 gallons. And there's nothing in the instructions that tell me what to do if it clogs - can I backflush? Do I need a second one as backup?
_________________________
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

http://hikeandbackpack.com