Most filter everything other than viruses. From what I've been told, viruses are more of a concern South of the border, in jungle areas. The owner manual that comes with your filter should tell you what it covers.

Any filter system will have a lower limit on the size of particles that it can filter, so the added step of boiling will always be advisable to make sure that you get viruses, smaller bacteria and cysts/spores that your filter may not handle. A VERY small quantity of bleach (like 1 small drop per gallon) or exposure to UV light can also help control some of those water-borne hazards, but boiling is still advisable.

You also have to weigh your immediate need for water - if you will die of thirst before you can get the chance to boil water, go with what your filter will give you and take your chances.

I would say boil the water..like they say "better safe than sorry"...but I would also reccomend to read the package to see what the filter covers.

boil anyway just to make sure, better safe then having diarreai.

I'd boil it regarless of what the filter said it could do.

boil the water when u can but it wont hurt u to drink straight out of a clean mountain stream

not to push my luck but ive used the katadyne pro or whatever the cheapest one is on numerous 4 day camping trips and without boiling ive had nothing but the freshest clearest tasteless water i think ever had. always use your best discresion

most can filter everything for the most part so you should be good.

Be safer to boil the water aswell. The bottle would do a good job though

I would boil it just to be safe

another purification process if you have none of the above is, believe it or not, whisky. It can make water completely safe after a given amount of time of course. See the survival issue of the backpacker for more details it's awesome.