Making water safe in an emergency: boil, disinfect, store
After floods, earthquakes or a broken water main, tap water may stop or become unsafe. CDC's guidance has three parts: store water before, make water safe during, and know what you can't fix.
How much to store
| Source | Guidance |
|---|---|
| CDC | At least 1 gallon per person per day for 3 days; a 2-week supply if possible. More for pregnant women, people who are sick, pets, or hot climates |
| Japan (MAFF) | About 3 liters per person per day for drinking and cooking, at least 3 days and preferably a week |
CDC calls unopened, commercially bottled water the safest and most reliable source in an emergency.
Storing your own water (CDC)
- Sanitize containers with 1 teaspoon of unscented household bleach in 1 quart (4 cups) of water.
- Label them "drinking water" with the date, and replace stored water every 6 months.
- Keep containers cool (50°F to 70°F), out of direct sunlight, and away from toxic substances such as gasoline or pesticides.
Japan's agriculture ministry gives a shorter rule for tap water stored in a clean container filled to the brim and tightly closed: thanks to chlorine, it stays drinkable for about 3 days.
Boiling
CDC says boiling is the best way to kill germs in water. Bring clear water to a rolling boil for 1 minute (at elevations above 6,500 feet, 3 minutes). If the water is cloudy, first filter it through a clean cloth, paper towel or coffee filter, or let it settle. Store boiled water in clean, sanitized containers with tight covers.
Disinfecting with bleach (CDC)
Follow the instructions on the bleach label if it has them. Otherwise, for typical U.S. household bleach (5% to 9% sodium hypochlorite):
| Amount of water | Bleach |
|---|---|
| 1 quart or 1 liter | 2 drops |
| 1 gallon | 8 drops (a little less than ⅛ teaspoon) |
| 5 gallons | 40 drops (½ teaspoon) |
Double the amount if the water is cloudy, murky, colored or very cold. Stir well and let it stand at least 30 minutes before drinking. CDC notes that disinfectants don't work as well as boiling against some parasites, including Cryptosporidium and Giardia.
What you can't fix
You cannot make water containing fuel, toxic chemicals or radioactive materials safe by boiling or disinfecting it. And never drink water from radiators or boilers that are part of your home heating system.
Our suggestions
- Keep bottled water in your rolling stock and drink the oldest first.
- At camp, practice boiling and treating water so it's routine.
- Use the household water and food calculator to size your supply.
Everyday
Keep bottled water in your rolling stock, and know how to boil and disinfect water at camp.
When it counts
If the water supply is cut or unsafe, you have water stored and know how to make more safe to drink.
Sources and when we checked them
- CDC, How to Make Water Safe in an Emergency (checked 2026-10-31)
- CDC, How to Create an Emergency Water Supply (checked 2026-10-31)
- MAFF (Japan), Disaster Food Stockpile Guide, ch. 5: Water (in Japanese) (checked 2026-10-31)
Spotted a mistake? Tell us through the contact form ("Report a mistake"). We check it, fix it, and log the change in Updates.