Water Treatment
Assume nothing is safe until treated
Clear mountain water can still carry organisms that lay you flat for days. When the safety of a water source is unknown, treat every drop before drinking, brushing teeth, or washing dishes that touch mouths.
At a glance
- Boil 1 minute below 6,500 ft; 3 minutes above.
- Unscented bleach, clear water: 8 drops per gallon at 6% strength, 6 drops at 8.25% — double drops if cloudy.
- Wait 30 minutes after dosing; a slight chlorine smell means success.
- Fuel/chemical smell or foam near industry: do not drink — chemical contamination survives boiling, filtering, and bleach.
Clarify first, then treat
Treatment works poorly in cloudy water. If water is murky:
- Let it stand so sediment settles (30–60 minutes helps a lot).
- Pour off the clearer top layer, or filter it through cloth, a coffee filter, or paper towel.
- Treat the clarified water using any method below.
Method 1 — Boiling (most reliable)
| Altitude | Time at rolling boil |
|---|---|
| Below 6,500 ft / 2,000 m | 1 full minute |
| Above 6,500 ft / 2,000 m | 3 full minutes |
No thermometer needed. Boiling kills everything that matters. Flat taste comes from lost air — shake the cooled water in a sealed jar or pour between two containers to restore it. Fuel-hungry, but unbeatable when fuel exists.
Method 2 — Unscented household bleach
Regular unscented liquid bleach only. Check the concentration percentage on the label:
| Bleach strength | Per gallon / 4 L | Per quart / liter |
|---|---|---|
| 6% | 8 drops | 2 drops |
| 8.25% | 6 drops | 2 drops (rounded down) |
- Add drops, stir, wait 30 minutes.
- Smell test: a slight chlorine smell means success. No smell? Repeat the dose and wait another 15 minutes.
Bleach has limits
Check your bottle: plain sodium hypochlorite 5–9%, unscented, not expired. Splash-less, thickened, scented, or "color-safe" formulas are not for water treatment. Bleach weakens with age — a bottle open over a year disinfects less reliably than its label claims.
Method 3 — Filters
What filters stop — and what slips past
- Good backpacking-style filters remove protozoa and bacteria — the most common wilderness troublemakers.
- Most squeeze/straw filters do not stop viruses, which matter mainly where human sewage contaminates water. After floodwater contact, boil or chemically treat even filtered water.
- Ceramic and charcoal countertop systems vary wildly by model; trust them only as far as their tested rating.
Sources ranked best to worst
- Rainwater caught in clean containers
- Moving water upstream of people and animals
- Lakes and ponds (surface scum — take water below it)
- Wells and taps of unknown status
- Floodwater, stagnant pools, water near latrines or industry — absolute last resort, treat twice
Do not drink at all
Any water with a fuel or chemical smell, foam or discoloration near industrial areas, or dead animals floating nearby. Chemical contamination does not boil out, filter out, or bleach away. Find another source.
After treating: keep it clean
Store treated water in scrubbed containers with tight lids, labeled with the date. Use within six months, rotating fresher stock forward — see Water Storage for container prep and quantities.
Grounded in public-domain CDC/EPA/FEMA emergency water guidance. Educational only — verify bleach percentages against your actual label.