Short answer, no.

The long answer is that most backpacking filters / straw type filters (that are vetted) are capable of filtering out larger biological threats, including oocysts like Cryptosporidium and common bacteria, but not viruses, which are typically too small for the filters to reliably stop.

As a result, common backpacking filters are an incomplete solution on their own if viruses are a potential threat. You will either have to treat chemically, use a UV purifier, or boil in addition to filtering to be positive. Incidentally, boiling and some (though not all) chemical treatments ARE stand alone solutions for the full spectrum of biological threats you're likely to encounter, but are generally less convenient on their own and of course won't help with other types of contaminants. Boiling requires you to be stationary, and of course requires fuel. Chemical treatments can be used while on the move, but iodine and chlorine based tablets are ineffective against oocysts due to their protective shell, and although chlorine dioxide based tablets will work, it can take an excessive amount of time (from 30 minutes to 4 hours depending on water conditions) in contrast to the ~15 minutes it takes to kill bacteria and viruses.

As a result, I find it's most convenient to filter first, then chemically treat with chlorine dioxide based tablets (or boil if I'm stationary).


Now and then a no name straw from China will pop up and claim to stop viruses, but then again these are the types of companies that claim their flashlights have a billion lumens. Perhaps there's a little iodine impregnated element inside someplace -- but considering the dwell time (basically zero) I wouldn't bet my health on it. Further, flow rates can be challenging even with larger diameter filters (Sawyer Mini, Lifestraw).

To be fair, viruses aren't always a major concern in the back country and hundreds of thousands of trekkers every year only filter and do just fine. The problem is, you simply can't tell just by looking at the water, and although rare, I don't like to take chances on something that's so easy to address -- so when there are humans (such as urban areas, and recreational areas where lots of hikers and travelers frequent), I always assume there is some degree of viral load in the water and treat accordingly just to be safe. One potential issue with a lot of hikers who only filter is that many may not carefully research the capabilities and limitations of their system and understand that there are potentially additional threats that are not biological in nature (such as contaminants), and some situations, in which filters will not help... but they'll often just buy a filter at the store and assume they're good to go anytime they need to make water safe.

Some examples where a backpacking filter that has served them well for years on the trail but may not render water safe to drink include post-disaster (especially in urban environments with flooding where there is often other contamination such as oil and fuel), traveling overseas to third world countries where viruses in the water are more prevalent than in the US, areas with industrial runoff, radiological threats and certain blue green algal blooms (not all algal blooms are harmful and have released the toxins, but there's no way to tell in the field and not even boiling will render those safe so it's better to avoid them entirely)

There are some more exotic filters that will filter out viruses, like the Sawyer point zero two, but these generally rely more on mechanical or gravity (and time!) to help push a useful amount of water through them making them incompatible with the "straw" approach, and they're also quite a bit bigger than most people want to carry backpacking. As such, they're more oriented towards home use.

Activated carbon filters can help with some of the other contaminants, heavy metals and toxins, but they rely on a certain amount of dwell time and volume to ensure adequate amounts of the contaminants have time to adsorb, and that's generally not something you're going to see backpacking. Besides, there's not really any way for you to measure contaminant levels pre and post filtering in the field to judge if it's safe. With that in mind, if a filter advertises a carbon element, it's generally to improve taste (which may certainly be worthwhile for palatability).

Hope it helps!