Water Purification Guide

Boiling is the most reliable method to kill pathogens. Bring water to a rolling boil.

1. Filter cloudy water through a clean cloth first.
2. Bring to a vigorous rolling boil.
3. Boil for the time indicated by your altitude (see calculator below).
4. Let cool naturally. Do not add ice.
5. Store in clean, sanitized containers.

Boil Time by Altitude

At higher altitudes water boils at lower temperatures, requiring longer boil times.

Bleach Disinfection

Use regular unscented liquid chlorine bleach (5.25–8.25% sodium hypochlorite).

If water is cloudy or very cold, double the amount. If no chlorine smell after 30 min, repeat the dose and wait 15 more minutes.

Iodine Tablets

• Follow package directions (typically 1 tablet per liter for clear water).
• Wait at least 30 minutes before drinking (longer in cold water).
• Not recommended for pregnant women or people with thyroid conditions.
• Effective against bacteria and viruses; less reliable against Cryptosporidium.
• Water may have a slight taste; vitamin C tablets can neutralize it after treatment time.

Tip: For best results in emergencies, combine methods (e.g., filter sediment first, then boil or use UV).

SODIS uses UV-A radiation from sunlight to destroy pathogens. Endorsed by the WHO for emergency use.

1. Use a clean, transparent PET plastic bottle (up to 2 liters). Remove labels.
2. Fill with clear water. If cloudy, pre-filter through cloth until you can read newspaper through the bottle.
3. Shake the bottle vigorously for 20 seconds with a small air gap to oxygenate.
4. Place horizontally on a reflective surface (corrugated metal roof is ideal) in direct sunlight.
5. Sunny/partly cloudy: 6 hours minimum.
6. Overcast: 2 consecutive days.
7. Rain/heavy clouds: Do not use SODIS; boil instead.
8. Drink directly from the bottle to avoid recontamination.

Does not remove chemical contaminants. Glass bottles block UV; use PET only.

Maintain a reliable emergency water supply with this checklist.