Safe drinking water
How much water to store and how to make water safe by boiling, bleach, filters or sunlight.
Quick card · Safe drinking waterSources checked 29 Oct 2026
Before
During
- Boil: bring clear water to a rolling boil for 1 minute, or 3 minutes above 6,500 ft. 1
- Bleach (5–9%): 8 drops per gallon. Double it if the water is cloudy, colored or very cold. Stir and wait at least 30 minutes. 1
- Cloudy water: let it settle or strain it through a cloth or coffee filter first. 1
- Water with fuel, toxic chemicals or radioactive material can't be made safe by boiling or bleach. Use another source. 1
Bleach amounts
| Water | Bleach 5–9% | Bleach 1% |
|---|---|---|
| 1 quart or liter | 2 drops | 10 drops |
| 1 gallon | 8 drops (about ½ mL) | 40 drops (about 2½ mL) |
| 5 gallons | 40 drops (about ½ tsp) | 200 drops (about 2½ tsp) |
Double the amount if water is cloudy, colored or very cold. Stir and let it stand at least 30 minutes. From the CDC. 1
Filters and tablets
- A filter needs a pore size of 0.3 micron or smaller to remove bacteria, and 1 micron or smaller for parasites. Filters do not remove viruses, so disinfect the water afterward. 1
- Iodine and chlorine tablets don’t kill Cryptosporidium. Chlorine dioxide tablets do, when used correctly. 1
- Avoid iodine-treated water if you’re pregnant, have thyroid problems or are sensitive to iodine, and don’t use it for more than a few weeks. 1
Sunlight
If nothing else is available, fill clean clear plastic bottles and lay them on their side in the sun for 6 hours, or 2 days if it’s cloudy. 1
Private wells
Test a private well every year for total coliform bacteria, nitrates, total dissolved solids and pH. Test again after flooding, after work on the well, or if the taste, color or smell changes. 3