Camping Water Purification Time Guide

Waterborne illness from untreated backcountry water is very real and very unpleasant.
Giardia and Cryptosporidium, the two most common backcountry pathogens, both survive happily in cold, clear mountain streams that look perfectly safe.

Boiling is the most reliable method and requires no equipment beyond a stove.
The key variable is altitude: water boils at lower temperatures as you go higher because atmospheric pressure decreases.
At sea level, water boils at 100°C (212°F).
At 3000 m (10000 ft), it boils at about 90°C (194°F).
Most pathogens die well before 100°C, but the reduced boiling temperature at altitude means the safety margin shrinks, so longer boil times are required.

CDC and WHO guidelines:

• Below 2000 m (6500 ft): 1 minute of rolling boil
• Above 2000 m: 3 minutes

UV treatment (SteriPen and similar devices) uses ultraviolet light to destroy the DNA of bacteria, viruses, and protozoa.
It works in 60-90 seconds for clear water but becomes ineffective in turbid (cloudy) water because particles block the UV rays.
If the water has suspended sediment, pre-filter through a bandana or coffee filter before using UV.

Chemical tablets (iodine or chlorine) kill bacteria and viruses but work more slowly, especially in cold water.
Cryptosporidium is resistant to iodine and to low-dose chlorine. Standard tablet doses do not kill it, whatever the box implies.
For chemical treatment that covers everything, use chlorine dioxide tablets rather than iodine or plain chlorine. They do work on Crypto, but they need 4 hours of contact time in cold water, which is the part people skip.

Elevation only changes the boiling answer. UV and tablets work the same at 4,000 m as at sea level, so the elevation dropdown below is there for the boiling case and is ignored for the rest.