Emergency Water Purification Basics
Boiling, filters, and bleach dosing — CDC-aligned methods when tap water is uncertain.
When to treat water
Treat drinking water when officials issue a boil-water advisory, after flooding near wells, or when taste/odor changes suddenly after infrastructure damage. CDC lists boiling, filtration, and disinfection as core approaches.
Boiling (most reliable household method)
Bring water to a rolling boil for 1 minute (3 minutes above 6,500 ft elevation). Let cool covered. Kills bacteria, viruses, and parasites — does not remove chemical contamination.
Filter + disinfect combo
Many portable filters remove bacteria and protozoa but not viruses. CDC notes some filters can be used with disinfectant steps — read manufacturer instructions. See boil vs filter decision guide.
Unscented bleach disinfection (clear water)
EPA emergency guidance for clear water: ⅛ teaspoon (8 drops) regular unscented household bleach per gallon, stir, stand 30 minutes, slight chlorine odor should remain. If cloudy, filter through cloth first or double dose per EPA tables — use official chart for your situation.
What does not work
- Pool chemicals not labeled for drinking water
- Saltwater desalination without proper equipment
- “Sun tea” disinfection alone in cloudy weather (SODIS has narrow conditions)
Key takeaways
- Boiling is the default gold standard at home.
- Filters vary — know virus rating before trusting alone.
- Chemical spills require official all-clear, not home filters alone.