Do gravity filters remove viruses, heavy metals, or just bacteria?

Most outdoor gravity filters (hollow-fiber 0.1 or 0.2 micron) are rated for bacteria and protozoa but not viruses, which matters more for international travel than North American backcountry water. Carbon-based countertop systems target chlorine, taste, and some heavy metals, but third-party lab testing surfaced in user communities has shown the actual lead and PFAS reduction varies widely by brand, so check for specific NSF/ANSI 53 certification rather than 42 or 372 alone.