TL;DR
Rolling boil for 1 minute (3 minutes above 6,500 feet elevation). That's the standard. A rolling boil, not a simmer — large bubbles breaking the surface continuously. This single step kills every biological pathogen in the water: bacteria, viruses, Giardia, Cryptosporidium. It does not address chemical contamination.
Boiling Time Reference
| Altitude | Boiling Point of Water | Required Boil Time | |---------|----------------------|-------------------| | Sea level - 6,500 ft | 212°F (100°C) | 1 minute rolling boil | | 6,500 - 13,000 ft | 194°F (90°C) | 3 minutes rolling boil | | Above 13,000 ft | ~185°F (85°C) | 3 minutes rolling boil |
Source: CDC emergency water treatment guidelines
Rolling boil vs. simmer: A rolling boil means large bubbles vigorously breaking the surface of the water — not small simmering bubbles at the bottom of the pot. Allow the boil to be vigorous and continuous for the full time.
Pathogens Killed by Boiling
| Pathogen | Killed by Boiling | |---------|------------------| | E. coli and other bacteria | Yes | | Salmonella, Campylobacter | Yes | | Giardia lamblia (cysts) | Yes (destroyed above 140°F/60°C) | | Cryptosporidium (oocysts) | Yes (destroyed above 140°F/60°C; 1 min boil is conservative) | | Hepatitis A virus | Yes | | Norovirus, rotavirus | Yes | | Cholera (Vibrio cholerae) | Yes | | All viruses | Yes (most inactivated above 160°F/71°C) |
Nothing biological survives a 1-minute rolling boil at appropriate altitude.
Containers for Field Boiling
Best options:
- Stainless steel water bottle or metal cup (put directly on coals or flame)
- Metal food cans (clean, remove lid, place on coals)
- Any steel or cast iron cooking pot
- Canteen cup (military issue; purpose-built for this)
Acceptable improvised options:
- PET plastic bottles (hold near flame rather than in it; keep moving; works in an emergency)
- Green bamboo section (green bamboo doesn't ignite immediately; fill with water and place at fire edge)
- Large clam or oyster shells (coastal environments)
Not suitable for direct flame:
- Glass (thermal shock risk)
- Aluminum foil alone (too thin; leaks at seams)
Fuel Estimate for Boiling Water
Rough estimate for bringing water to boil and maintaining rolling boil for 1 minute, with a small efficient fire:
| Volume | Approximate Fuel Needed (dry hardwood) | |--------|---------------------------------------| | 1 cup / 8 oz | A handful of pencil-diameter sticks | | 1 quart / 32 oz | A forearm-length of wrist-diameter wood | | 1 gallon / 128 oz | Approximately 1 lb of dry wood |
These estimates assume an efficient fire with good coals. Poor fire management — too much green wood, inadequate airflow, large fire for a small pot — multiplies fuel consumption.
Dakota fire hole efficiency: The same volume of water requires approximately 40-50% less fuel in a Dakota fire hole versus an open fire due to more complete combustion and direct heat transfer to the pot.
Cloudy Water
Boiling kills biological pathogens but doesn't clarify visually cloudy water. Turbid water carries particulates that may harbor pathogens and can interfere with chemical treatment methods.
Pre-filter cloudy water before boiling:
- Allow to settle in a container for 15-30 minutes; decant the clearer upper portion
- Filter through layers of cloth, clean sand, or crushed charcoal
- Then boil the filtered water
Very turbid water filtered and boiled is safe to drink. Turbid water boiled without filtering may still carry sediment (harmless but unpleasant).
Chemical Contaminants
Boiling concentrates dissolved chemicals by reducing water volume through evaporation. If water is suspected of chemical contamination (odor of petroleum, industrial area, old mine drainage), boiling alone is not a solution.
Activated charcoal filtration reduces many organic chemical contaminants. No field method fully addresses heavy metal contamination. In these situations, finding an alternative water source (rainwater, deep well) is preferable to treating surface water of unknown chemical quality.
Sources
Frequently Asked Questions
How long do you need to boil water to make it safe?
The CDC recommends bringing water to a rolling boil for 1 minute at altitudes below 6,500 feet (2,000 meters). At altitudes above 6,500 feet, boil for 3 minutes — the lower boiling point at altitude (below 212°F) requires longer contact time to achieve the same pathogen kill. One minute of rolling boil is sufficient to kill all biological pathogens including bacteria, viruses, and parasites (Giardia, Cryptosporidium). It does not remove chemical contaminants.
What does boiling not remove from water?
Boiling kills or inactivates all biological pathogens. It does NOT remove: heavy metals (lead, arsenic, mercury), chemical contamination (pesticides, fuels, industrial chemicals), salt, sediment, or other dissolved minerals. If water may be chemically contaminated (near industrial sites, agricultural runoff, abandoned mines), boiling alone is not sufficient. Filter through multiple layers of charcoal and allow to settle before boiling if chemical contamination is suspected.
Can you boil water in improvised containers?
Metal containers of any kind work — metal cans, metal bottles, steel cups. Plastic bottles work when held in moving water with a small fire close to the water surface (the water absorbs heat before the plastic overheats). Bamboo sections work in a pinch. Clay pots work if thick enough. Bark containers with stone boiling work (see stone boiling in the cooking fire article). Glass works but thermal shock from direct flame can shatter it — place in already-hot water rather than directly on flame.