Keep an emergency treatment backup
Power cuts, broken UV units or contamination events happen. Know how to make water safe without your main system.
How
- Boiling: CDC says hold a rolling boil for 1 minute, or 3 minutes above 2,000 m (6,500 ft).
- US EPA says 3 minutes above 5,000 ft and lists this as 1,000 m, although 5,000 ft is about 1,500 m. To be safe, boil 3 minutes above 1,000 m.
- Bleach: check the strength on the label first. CDC doses for 1 percent bleach are five times those for 5 to 9 percent bleach.
- 5 to 9 percent unscented bleach: 2 drops (0.1 mL) per litre, or 8 drops per US gallon (CDC).
- 1 percent bleach: 10 drops (0.5 mL) per litre, or 40 drops per US gallon (CDC).
- Double the dose for cloudy, murky, coloured or very cold water. Stir and wait at least 30 minutes before drinking (CDC).
- Smell test: after 30 minutes the water should smell slightly of chlorine. If not, repeat the dose and wait another 15 minutes (US EPA; HealthLinkBC, Canada).
- Avoid scented, colour-safe or non-chlorine bleach (HealthLinkBC). If you cannot find the strength, boil instead. For other volumes, use the chlorine dose calculator.
- Filter cloudy water through a cloth or let it settle before treating (CDC, US EPA).
- Chlorine dioxide products, used as labelled, kill Cryptosporidium; iodine and standard chlorine tablets do not (CDC).
- Store fresh bleach (US EPA says less than a year old) and a backup filter or boiling fuel.
- Remember none of these remove metals, salts or most chemicals (US EPA).
Safety: Avoid iodine-treated water if pregnant or with thyroid problems, and no one should use it for more than a few weeks (CDC).
Do these first
Sources
- 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
- HealthLinkBC File 49b: Disinfecting drinking water (July 2025). HealthLinkBC, Government of British Columbia (Canada), accessed 2026-11