Jim, That is a general question to anyone using a pump filter system. I've never had to use a secondary filter or purify any further. I only filter mountain stream water, above 9,000 ft, & have never been sick either. When above 12,000 ft I don't filter @ all in clean moving streams or water coming directly out of rocks. If you're trying to kill/remove viruses, you'll have to use a purifying system like the SteriPen, First Need, chlorine dioxide tablets, Polar Pure, etc.

Jeff is that a question to me or others? (Do the people that use a pump filter system further treat their water with a "SteriPen" or tablets?) I would tend to trust the water after filtering rather than not especially in some of the mountain streams I would use (I have also never been sick from water) however a video I watched does say that it does not filter virus so just curious how concerned I should be with further treatment.

I've been using this system all summer with very positive results. I trust it just as much as a pump filter. Look @ it this way, gravity is gently moving the water through the filter rather than me forcing it through with a pump. Do the people that use a pump filter system further treat their water with a "SteriPen" or tablets? The filter element is good for a subjective 1500 liters.