Water Purification Time Calculator
Get safe boiling times for water purification by altitude. Per CDC guidelines, boil for 1 minute at low altitude, 3 minutes above 6,500 ft.
Quick Answer
CDC guidance: boil water for 1 minute at a rolling boil. Above 6,500 ft (2,000 m), boil for 3 minutes because lower boiling temperatures slow pasteurization. Boiling kills bacteria, viruses, and protozoa.
Guidance
At elevations above 6,500 ft (2,000 m), boil for at least 3 minutes at a rolling boil. The lower boiling point reduces pasteurization efficiency, requiring extra time.
Boil Time Reference Table
| Altitude | Boiling Point | Boil Time |
|---|---|---|
| 0 ft | 212.0°F | 1 min |
| 1,000 ft | 208.4°F | 1 min |
| 3,000 ft | 201.2°F | 1 min |
| 5,000 ft | 194.0°F | 1 min |
| 6,500 ft | 188.6°F | 1 min |
| 8,000 ft | 183.2°F | 3 min |
| 10,000 ft | 176.0°F | 3 min |
| 12,000 ft | 168.8°F | 3 min |
| 14,000 ft | 161.6°F | 3 min |
About This Tool
The Water Purification Time Calculator gives you the boiling time you need to safely purify backcountry water based on your altitude. The CDC and WHO guidelines are clear: 1 minute at a rolling boil at low elevations, 3 minutes above 6,500 ft (2,000 m). This tool also shows the actual boiling point at your elevation — useful for understanding why higher altitude needs longer boil times.
Why Boiling Works
Boiling pasteurizes water by exposing it to high temperatures long enough to kill or inactivate all common waterborne pathogens. Bacteria like E. coli die at 158°F (70°C) within minutes. Giardia cysts die at 158°F within 5 minutes. Cryptosporidium oocysts, the toughest common pathogen, are inactivated at 161°F within 2 minutes. A rolling boil exceeds all these thresholds with margin, making the time-at-temperature requirement quite short.
Why Altitude Changes the Math
Atmospheric pressure decreases with elevation, and water's boiling point depends on pressure. At sea level (1 atm), water boils at 212°F. At 5,000 ft (~0.83 atm), it boils at about 203°F. At 10,000 ft (~0.69 atm), it boils at about 194°F. Even at 194°F, all pathogens still die — but slower. The CDC's 3-minute recommendation above 6,500 ft adds margin for slower pasteurization at the lower temperature.
The CDC Standard
Centers for Disease Control and Prevention guidelines: bring water to a rolling boil for 1 minute at altitudes up to 6,500 ft (2,000 m), and 3 minutes above 6,500 ft. A “rolling boil” means continuous, vigorous bubbling — not just simmering. The full minute starts when the rolling boil begins, not when bubbles first appear. WHO and EPA guidelines align with these numbers.
What Boiling Doesn't Remove
Boiling is excellent against living pathogens (bacteria, viruses, protozoa) but useless against chemical contaminants. Heavy metals (lead, mercury, arsenic), pesticides, herbicides, mining runoff, and petroleum products all survive boiling. If you suspect chemical contamination — proximity to old mines, agricultural runoff, road salt, fracking — boiling is insufficient. Use an activated carbon filter, find a different source, or pack in water from a known-clean source.
Filters vs. Boiling vs. Chemicals vs. UV
Each method has tradeoffs. Boiling: reliable, no consumables, slow, uses fuel. Filters (Sawyer, Katadyn): fast, no fuel, but can clog and most miss viruses. Chemicals (Aquamira, iodine): light and reliable but slow (30-60 min wait time) and bad-tasting. UV (SteriPEN): fast and tasteless but battery-dependent and requires clear water. Most experienced backpackers carry two methods: a primary (filter) and a backup (chemicals or boiling capability).
Boiling at Altitude With a Stove
Canister stoves work poorly in cold and at altitude — fuel doesn't vaporize as effectively. Liquid fuel stoves (MSR Whisperlite) work better in extreme conditions. To save fuel: use a windscreen, cover the pot, and don't over-boil. Bringing 1 liter of cold water to a rolling boil takes 3-6 minutes and burns 8-15g of fuel depending on conditions. Plan fuel: 8oz canister covers about 5-7 days of cooking and water purification for one person.
Plan Your Trip
Pair this with our altitude sickness risk calculator, our hike water needs calculator, our backpacking food weight calculator, and our hiking time calculator.