What are the different methods of purifying water?
The main ways to make water safe are boiling, chemical disinfection, filtration, UV light and solar disinfection. According to the CDC, boiling for 1 minute (3 minutes above 6,500 feet) is the standard method for clear water. No home method removes fuel or toxic chemicals.
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In this article
Boiling
Bring clear water to a rolling boil for 1 minute, or 3 minutes above 6,500 feet. Let it cool and store it in clean covered containers. Boiling does not remove fuel, toxic chemicals or radioactive materials.
Household bleach
Use plain bleach with 5% to 9% sodium hypochlorite. For clear water add 2 drops per quart or liter, 8 drops per gallon, or 40 drops (a half teaspoon) per 5 gallons. Double the amount if the water is cloudy, colored or very cold. Stir, then wait at least 30 minutes before drinking. Use the CDC chart for weaker 1% bleach, because the drop counts are different.
Tablets or drops
Follow the product label. They kill viruses and bacteria but may not kill parasites. Chlorine dioxide kills Cryptosporidium if used correctly; iodine and chlorine tablets do not. Avoid iodine if you are pregnant, have thyroid problems or are sensitive to it.
Portable filters
Filters do not remove viruses. For bacteria, the pore size must be 0.3 micron or smaller. For parasites such as Giardia and Cryptosporidium, 1 micron or smaller. After filtering, add a disinfectant to deal with viruses and bacteria.
UV light and solar disinfection
UV works only on clear water, so filter cloudy water first and follow the device instructions. For solar disinfection, fill clean clear plastic bottles with clear water and lay them in the sun for 6 hours if sunny or 2 days if cloudy.
| Method | Kills germs | Removes chemicals |
|---|---|---|
| Boiling | Yes | No |
| Bleach / tablets | Viruses, bacteria (parasites vary) | No |
| Filter alone | Bacteria, parasites if pore size right; not viruses | Depends on the filter |
When to ask for help
If water may be contaminated with fuel or chemicals, find another source. For city water advisories, follow your local health authority.
People also ask
How long should you boil water to purify it?
One minute at a rolling boil, or 3 minutes above 6,500 feet, according to the CDC.
Does a water filter make water safe to drink?
Not by itself. Filters do not remove viruses, and the pore size must be 0.3 micron or smaller for bacteria and 1 micron or smaller for parasites.
Does boiling remove chemicals from water?
No. Boiling does not remove fuel, toxic chemicals or radioactive materials.
Sources
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