The fastest way to ruin a backcountry trip is to drink unfiltered water. Giardia, Cryptosporidium, E. coli — none of them announce themselves at the source. The water in a clear alpine creek looks identical to the water that will keep you on the toilet for two weeks. Treat all backcountry water. There are three reliable ways to do it; pick the one that fits your trip.
Filter (mechanical)
A pump filter or squeeze filter (Sawyer Squeeze, Katadyn BeFree, MSR Trail Shot) physically removes pathogens via a fine-pore membrane. They work fast, taste good, and don't require waiting. They don't kill viruses, but viruses are essentially never present in US wilderness water (different in Mexico/Asia).
Best for: most US trips, fast water access, groups.
Watch out for: filters freeze, and a frozen filter is broken. In winter, sleep with it in your sleeping bag.
Chemical (drops or tablets)
Aquamira drops (chlorine dioxide) or Potable Aqua tablets (iodine) kill all bacteria, viruses, and protozoa given enough contact time. Lightweight, simple, no moving parts. Tradeoff: you have to wait 30 minutes (Aquamira) or 4 hours (against Crypto), and the taste is medicinal.
Best for: backup to a filter, ultralight setups, international travel.
Watch out for: cold water increases contact time. In near-freezing water, double the wait.
Boil
Three minutes at a rolling boil kills everything that can hurt you. Adds elevation? Boil longer (at altitude, water boils at lower temperatures, so you need more time). Always works, no equipment beyond your stove and pot.
Best for: cooking water anyway, base camp use, when filters fail.
Watch out for: fuel cost. Boiling all your drinking water adds up quickly.
The combined kit we recommend
- Sawyer Squeeze or BeFree filter as your primary.
- Aquamira drops as a backup — fits in a film canister.
- The ability to boil via your camp stove for any water that's questionable looking (cloudy, milky, near beaver activity).
The best water purification system is two systems. Always have a backup, because the moment you need water clean is the moment your filter clogs.
Source selection still matters
Even with treatment, draw water from the cleanest source you can reach. Avoid water below pack stock fords, beaver activity, dead carcasses, or downstream of obvious algae. A clear source running fast over rocks is your friend; a stagnant pool with surface scum is your enemy even after treatment.
Hydration matters more than you think
At altitude, in dry air, on a moving body, you'll lose 4-6 liters of water a day without sweating heavily. By the time you're thirsty, you're already 1-2% dehydrated and your performance is dropping. Drink ahead of thirst.
For hydration systems and filtration tools, shop the kit.