I believe Walmart sells the Sawyer Point Zero Two water filter bottle. Sawyer claims it has 0.02 micron absolute filtration efficiency, which would be sufficient to remove viruses as well as bacteria and protozoa. I don't have anyway to verify the efficiency other than saying my son used it in Ecuador two summers ago and I've used it frequently since, and neither one of us ever got sick. It does take some effort to draw water, more as it is used, but when you get home it's easy to backflush it back to original from your faucet, and disinfect it if needed using dilute bleach.
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I didn't like the bottle it came in. The bottle is larger than a Nalgene and wouldn't fit in my stainless steel cup, and I didn't like the the Sawyer cap design either. So I took the filter out and fit it to the Bite-N-Flip cap from a Camelbak bottle, then trimmed the hose so the whole thing fit on to a standard Nalgene.
You can also remove the filter and hook it in-line with a hydration bladder, both to such through and even as a gravity filter. I tried the gravity filter and it was slow but worked.