How to make water safe to drink in an emergency
The short answer
Bottled water is the safest choice. If you don't have any, the CDC says to boil clear water at a rolling boil for 1 minute, or 3 minutes above 6,500 feet. If you can't boil it, add unscented household bleach, about 8 drops per gallon, stir and wait at least 30 minutes. Neither one makes water safe if it has fuel or toxic chemicals in it.
Pick your method
| Method | Best for | Watch out for |
|---|---|---|
| Boiling | The surest way to kill germs, including the parasites Giardia and Cryptosporidium | You need power or fuel and a pot |
| Unscented bleach | No power, or large amounts of water | May not kill parasites. Use the right amount for your bleach. |
| Chlorine dioxide tablets | Your kit or a go-bag | Follow the label exactly |
| Iodine or chlorine tablets | Your kit or a go-bag | Don't kill Cryptosporidium. Avoid iodine if you're pregnant or have thyroid problems. |
| Portable filter | Removing parasites and, with a fine filter, bacteria | Doesn't remove viruses. Disinfect the water after filtering. |
How to boil water
- If the water is cloudy, filter it through a clean cloth, paper towel or coffee filter, or let it settle and pour off the clear water on top.
- Bring it to a rolling boil for 1 minute. Above 6,500 feet, boil it for 3 minutes.
- Let it cool.
- Store it in clean, sanitized containers with tight covers.
Boiled water can taste flat. The CDC's tip: pour it back and forth between two clean containers and let it stand for a few hours, or add a pinch of salt per quart or liter.
How to disinfect water with bleach
Use regular, unscented household chlorine bleach. Check the label: most U.S. bleach is 5% to 9% sodium hypochlorite. If the label gives directions for disinfecting drinking water, follow those.
Bleach calculator
8drops
That's 0.5 mL, or a little less than ⅛ teaspoon. Stir, then wait at least 30 minutes before you drink it.
The calculator uses the CDC's table: for 5–9% bleach, 2 drops per quart, 8 drops per gallon and 40 drops for 5 gallons. For 1% bleach, it's five times as much. Double it if the water is cloudy, murky, colored or very cold.
- Use a clean dropper if you have one. Drops are easier to get right than spoons for small amounts.
- Stir it well and let it stand for at least 30 minutes before you drink it.
What boiling and bleach can't fix
The CDC is clear: boiling and disinfecting won't make water safe if it has fuel, toxic chemicals or radioactive material in it. If you think your water is contaminated that way, use bottled water or another source, and call your local health department.
Until your water is safe, don't use it to drink, brush your teeth, wash dishes or hands, make ice, prepare food or mix baby formula. Our guide to water for babies covers formula.
Store water now so you don't have to treat it
Treating water is the backup plan. The easy plan is clean water stored before you need it. The water storage calculator tells you how much your household needs, and our guide to hidden water in your home shows where to find more.