There’s no doubt that boiling water makes it safe to drink—the high temperature kills all the aquatic baddies that might otherwise make you sick in the backcountry. But how long do you really need to boil water before its safe?

Over the years I’ve heard any number of recommendations, from 5 minutes, to 1 minute, to just enough to get “fish-eye” bubbles on the bottom of your pot. If I’m boiling water for dinner in the backcountry, I often prefer the convenience of not filtering it or adding a chemical treatment beforehand. To conserve fuel, I want to minimize the amount of time I have to boil it to be safe. Here’s what I’ve learned.

Water temperatures above 160 degrees Fahrenheit kill virtually all pathogens within 30 minutes, including bacteria and the two prime backcountry nemeses: giardia and cryptosporidia. At 185 degrees Fahrenheit, they’re dead in just a few minutes. Almost nothing can survive sea-level boiling temperature (212° F) for any length of time, though a few pathogens like botulism can persist at even higher temperatures (none that are a concern in the backcountry).

Keep in mind that boiling temperature decreases with altitude at roughly one degree per 500 feet. So on top of Mount Washington (6,288 feet), the boiling temperature will be almost exactly 200 degrees F. If you’re traveling to high country outside of the Northeast, boiling temps can be as low as 195 degrees F (9,000 feet) or 190 degrees F (12,000 feet).

So what’s the upshot? Most health organizations, including the Center for Disease Control, recommend that you boil water vigorously for 1 minute up to elevations of 2,000 meters (6,562 feet) and 3 minutes at elevations higher than that. You’re guaranteed to be safe from giardia and crypto if you follow those guidelines.

Here’s my personal take on the matter. At lower elevations (anywhere in the Northeast certainly), I always achieve a rolling boil at a minimum. “Fish eye” bubbles don’t cut it since they aren’t an indication that all of the water has reached boiling point. If you turn off the heat the second it starts to boil, the time it took to go from 185 degrees F to boiling will almost surely have killed all the baddies in the water. However, one extra minute is a small price to pay and I usually go for the extra 60 seconds for ultimate peace of mind.