The Church used to sell Seychelle water bottles. They were inexpensive but effective. The neat thing is Seychelle had four different filters you could swap out. Their Extreme filter not only filtered viruses (which isn't common) but also radiation. This is the ONLY water filter I know of that filters radiation...for whatever that's worth.

The Church now sells WaterBasics bottles. They are similar to the Seychelle, but come with a virus-capable filter. It only costs $29.25 online.