Emergency treatment guide • Updated October 2026
What Boiling Water Kills—and What It Doesn’t
Boiling is the CDC’s preferred household method for killing germs, but it does not remove chemical contamination, salt, or heavy metals.
The short answer
Bring clear water to a full rolling boil for one minute. At elevations above 6,500 feet, boil for three minutes. Let it cool without adding ice or untreated water, then store it in a clean, sanitized container with a tight cover.
What boiling kills
Boiling kills disease-causing viruses, bacteria, and parasites. This includes organisms that ordinary chemical disinfection or common pitcher filters may not reliably handle. During a boil-water advisory, the CDC says to boil tap water even if it has passed through a home or pitcher filter.
| Organism type | Examples | Killed by proper boiling? |
|---|---|---|
| Bacteria | E. coli, Salmonella, Shigella, cholera | Yes |
| Viruses | Norovirus, hepatitis A, rotavirus | Yes |
| Parasites | Giardia and Cryptosporidium | Yes |
The correct boiling method
- If water is cloudy, let it settle and filter the clearer portion through a clean cloth, paper towel, or coffee filter.
- Bring the clear water to a full rolling boil with vigorous, continuous bubbling.
- Continue boiling for one full minute—or three minutes above 6,500 feet.
- Turn off the heat and allow the water to cool naturally.
- Transfer it using clean utensils into sanitized containers with tight covers.
What boiling does not remove
- Fuel and industrial chemicals: boiling is not a cleanup method for spills or contaminated floodwater.
- Pesticides and many toxins: some remain in the water.
- Lead, arsenic, mercury, and other metals: these do not disappear when germs are killed.
- Nitrate: boiling does not remove it and evaporation can increase its concentration.
- Salt: seawater remains salty unless the vapor is captured through a proper distillation process.
As water evaporates, dissolved contaminants may remain behind in a smaller volume. If fuel, chemicals, toxins, or salt may be present, use another known-safe source and follow official instructions.
Boil-water advisory versus do-not-drink advisory
Boil-water advisory
Use bottled water or correctly boiled water for drinking, cooking, preparing beverages, making ice, and brushing teeth. Follow the local notice for dishes, bathing, infant feeding, pets, and other uses.
Do-not-drink advisory
Do not assume boiling solves the problem. These notices may involve chemicals or toxins. Use the source officials specify—often commercially bottled water—and follow the advisory exactly.
Fuel and heat-source planning
Boiling requires more than a pot: it requires a heat source that is safe, legal, ventilated, and available throughout the outage. Actual fuel use varies widely with water temperature, pot size, lid use, wind, burner design, elevation, and stove efficiency, so universal “gallons per tank” promises are unreliable.
- Store safe water first so you are not forced to boil every gallon immediately.
- Use a lid and heat only the amount needed for drinking, cooking, brushing teeth, and other advisory-covered uses.
- Follow the appliance instructions and keep combustibles away.
- Never use a grill, camp stove, generator, or other fuel-burning outdoor appliance inside a home, garage, tent, or enclosed space. Carbon monoxide can kill without warning.
- Keep a non-flame backup, such as labeled chemical disinfectant, for situations where boiling is impossible.
Cooling and storage
Let boiled water cool on its own. Do not add questionable ice or untreated water. Store it in clean, sanitized containers with tight covers, avoid touching the inside of the container or lid, and use a clean pouring or dispensing method. Boiling does not prevent later recontamination.
If the taste seems flat, CDC guidance suggests pouring cooled water between two clean containers and then letting it stand for a few hours, or adding a small pinch of salt per quart or liter if medically appropriate.
Frequently asked questions
Does boiling water fully purify it?
No. It disinfects by killing germs. It does not remove salt, metals, or many chemicals and toxins.
How long should water boil?
One minute at a full rolling boil, or three minutes above 6,500 feet, according to the CDC.
Should filtered tap water still be boiled during an advisory?
Yes, unless local officials give different instructions. The CDC specifically says to boil tap water even if it has passed through a home or pitcher filter.
Can I boil floodwater?
Floodwater can contain sewage and chemical hazards. Boiling may kill germs but will not remove chemicals. Use bottled or another approved source whenever possible and follow public-health directions.
Can I use a propane grill indoors to boil water?
No. Grills and other outdoor combustion appliances can produce deadly carbon monoxide and must not be used indoors or in enclosed spaces.
Keep a second treatment method
Stored water and a labeled disinfection method provide backups when fuel, ventilation, weather, or equipment makes boiling impractical.
Sources
Boiling time, altitude adjustment, advisory use, cooling, storage, and chemical-contamination limits follow CDC emergency-water guidance and the CDC advisory overview.