A filter is a useful tool, but its marketing should never be mistaken for a guarantee that any water is safe.
Match the filter to the problem
Different products target different hazards. Some hiking filters are designed mainly for bacteria and protozoa, while viruses, dissolved chemicals, industrial contamination or salt may require other treatment methods. Check the specific product's independently supported performance claims.
Use public-health guidance
During a local boil-water advisory or a known contamination event, follow your municipality's instructions. Do not assume an ordinary filter replaces boiling or disinfection. Keep a store of safe drinking water as the first line of defence.
Practice maintenance
Learn how to backflush, clean, store and protect the filter from freezing as required by its manufacturer. A filter that has been damaged or stored improperly may not perform as expected.