Choose household water treatment that works without power
When pumps, UV lamps and pressure fail, you need treatment that runs on fuel, sun, chemicals or gravity. Own at least two methods, so one failure does not leave you stuck.
How
- Prefer products tested under the WHO household water treatment scheme. Three stars means at least 4 log (99.99%) removal of bacteria, 5 log of viruses and 4 log of protozoa (WHO).
- Two stars means at least 2 log of bacteria, 3 log of viruses and 2 log of protozoa. One star protects against only two of the three germ groups (WHO).
- Boiling needs only fuel and a pot. See water-25 for boiling times (CDC).
- Chlorine (bleach or tablets) is cheap, but Cryptosporidium is poorly killed by chlorine or iodine at practical doses (CDC Yellow Book).
- Chlorine dioxide kills Cryptosporidium at practical doses and contact times (CDC Yellow Book). Use it exactly as labelled.
- Filters: microfilters under 1 micron remove bacteria and protozoa but not viruses reliably. Ultrafilters of about 0.01 micron also remove viruses (CDC Yellow Book).
- With a microfilter only, add chlorine or boiling where viruses are a risk.
- Ceramic filters can be made locally, but carbon-only filters are generally not rated for germs (CDC Yellow Book). Look for a WHO scheme rating or a tested germ removal claim.
- Solar disinfection (SODIS): fill clear plastic bottles with clear water. Lay them on their side in full sun for at least 6 hours, shaking now and then (CDC Yellow Book).
- In cloudy weather, leave SODIS bottles out for 2 days in a row, and clarify very cloudy water first (CDC Yellow Book).
- Iodine: people with unstable thyroid disease or iodine allergy should not use it. Pregnant women should not use it for long periods (CDC Yellow Book).
- None of these methods remove salts, metals or most chemicals (US EPA). Keep stored water for chemical problems (water-32).
Safety: Boiling, chlorine and filters do not remove fuel, chemicals or salts (US EPA). Do not drink water you suspect is chemically contaminated.
Do these first
Sources
- International Scheme to Evaluate Household Water Treatment Technologies: products evaluated. World Health Organization, accessed 2026-11
- CDC Yellow Book: Water disinfection for travelers. US Centers for Disease Control and Prevention (CDC), accessed 2026-11
- How to Make Water Safe in an Emergency. US Centers for Disease Control and Prevention (CDC), accessed 2026-11
- Emergency Disinfection of Drinking Water. US EPA, accessed 2026-11