How to treat water
- 1Collect the clearest water you can — flowing over rock beats stagnant; avoid green, algae-laden water if you have a choice.
- 2Pre-filter if cloudy — pour through a cotton cloth or coffee filter to remove sediment and algae.
- 3Pick a method for the risk: boil for the most complete kill (including cryptosporidium) — bring it to a rolling boil; filter (1-micron absolute) to remove giardia and cryptosporidium, remembering it won't stop viruses; or chemical tablets where boiling or filtering isn't practical.
- 4Combine in virus-risk areas — filter first, then treat the filtered water chemically (or boil) to kill viruses.
- 5Let it work — don't drink chemically treated water before its full contact time is up (treating overnight is an easy way to hit long contact times).
- 6Keep treated and untreated water separate — wipe bottle threads and caps so raw water can't re-contaminate a clean bottle.
Follow current guidance for times. Use the current CDC / Wilderness Medical Society standards for how long to hold a rolling boil (it changes with altitude) and your product's own contact times. This page names methods, not exact times or chemical doses.
When to use it
- Any backcountry trip where you refill from streams, lakes, or springs.
- Group treatment — gravity filters or boiling large pots at a base camp.
- Emergency backup — knowing boiling alone makes water safe when a filter clogs or tablets run out.
Common mistakes & safety
- Untreated water is a real illness risk. Giardia and cryptosporidium cause days of vomiting and diarrhea and dangerous dehydration — treat every backcountry source, however clean it looks.
- Know each method's blind spot. Filters miss viruses; chemicals are unreliable on cryptosporidium; boiling handles both — match the method to the risk, and combine when unsure.
- Give chemicals their full time. Under-timing (especially in cold or cloudy water) leaves live pathogens — wait the full contact time; don't shortcut it because you're thirsty.
- Pre-filter and use fresh tablets. Cloudy water and stale tablets both undercut treatment.
- Don't cross-contaminate. After treating, clean the bottle threads and cap so raw water on them doesn't re-infect the clean water.
- This is health guidance — verify current standards. Follow current CDC / Wilderness Medical Society and product directions for exact boil and contact times.
Going deeper
- Boiling is the fail-safe. It's heavy on fuel and slow, but it's the one method with no blind spot — worth knowing when gear fails.
- Filter + chemical = belt and suspenders. The filter takes out the parasites a chemical struggles with (crypto); the chemical kills the viruses a filter can't catch.
- Treat overnight. Long chemical contact times are painless if you set a bottle to treat before bed and drink it in the morning.
Official source
How to purify water, no matter where you are — Scouting Magazine →Health guidance — confirm all methods and times against current CDC / Wilderness Medical Society standards, and follow your product's directions.