By name: purify-water locale: caveman-ultra source_locale: en source_commit: 82c77053 translator: "Julius Brussee homage — caveman" translation_date: "2026-04-26" description: > Purify water from wild sources via boiling, filtration, chemical methods. Source assessment + priority ranking, sediment pre-filter, method selection (boiling, chemical, UV, filter), altitude-adjusted boiling, chemical dosages, safe storage. Use → wilderness drinking water, unknown quality sources, emergency dehydration risk, water safe for cooking or wound cleaning. license: MIT allowed-tools: Read metadata: author: Philipp Thoss version: "1.0" domain: bushcraft complexity: intermediate language: natural tags: bushcraft, water, purification, survival, wilderness, filtration
Purify Water
Purify wild sources → safe drinking water via field-available methods.
Use When
- Need drinking water in wilderness, no treated water access
- Sources unknown quality (streams, rivers, lakes, ponds)
- Emergency survival, dehydration risk
- Water safe for cooking or wound cleaning
In
- Required: Water source (flowing or still)
- Required: Container (metal pot, bottle, improvised)
- Optional: Purification supplies (chemical tablets, filter, UV pen)
- Optional: Fire-making for boiling (see
make-fire) - Optional: Cloth or natural filter materials for pre-filter
Do
Step 1: Assess + Select Source
Not all sources equal risk. Pick best available.
Water Source Priority Ranking (best to worst):
┌──────┬─────────────────────────┬────────────────────────────────────┐
│ Rank │ Source │ Notes │
├──────┼─────────────────────────┼────────────────────────────────────┤
│ 1 │ Spring (at the source) │ Lowest contamination; still treat │
│ 2 │ Fast-flowing stream │ Moving water has fewer pathogens │
│ │ (above human activity) │ than still water │
│ 3 │ Large river │ Dilution helps but agriculture/ │
│ │ │ industry upstream is a concern │
│ 4 │ Large lake │ Collect from open water, not shore │
│ 5 │ Small pond or puddle │ High pathogen and parasite risk │
│ 6 │ Stagnant pool │ Last resort; heavy treatment needed│
└──────┴─────────────────────────┴────────────────────────────────────┘
Warning Signs (avoid if possible):
- Dead animals nearby
- Algae bloom (blue-green scum)
- Chemical odor or oily sheen
- Downstream of mining, agriculture, or settlements
- No surrounding vegetation (may indicate toxic soil)
Collect below surface (avoid surface film), away from bank edge.
→ Clear or slightly turbid water from best available source, in clean container.
If err: only poor sources available (stagnant, turbid) → proceed but plan aggressive pre-filtering (Step 2) + multiple methods (belt-and-suspenders). No source found → look for indicators: green vegetation in valleys, animal trails downhill, insect swarms at dawn/dusk, listen for running water.
Step 2: Pre-Filter Sediment
Remove particulate before purification. Sediment reduces chemical effectiveness + clogs filters.
Improvised Gravity Filter (layered in a container with a hole at the bottom):
┌─────────────────────┐ ← Open top: pour water in
│ Grass / cloth │ ← Coarse pre-filter
│ Fine sand │ ← Removes fine particles
│ Charcoal (crushed) │ ← Adsorbs some chemicals and odors
│ Gravel │ ← Structural support
│ Grass / cloth │ ← Prevents gravel from falling through
└────────┬────────────┘
│
Filtered water drips out
Materials:
- Container: birch bark cone, hollow log, cut plastic bottle, sock
- Sand: fine, clean sand (rinse first if possible)
- Charcoal: from a previous fire (NOTite ash — charcoal only)
- Gravel: small stones, rinsed
Simple sediment removal → strain through bandana, t-shirt, multiple cloth layers.
→ Visibly clearer water, reduced turbidity. Charcoal removes some odor + taste.
If err: still very turbid after filtering → settle 30-60 min. Carefully decant clearer top layer. Repeat. Note: pre-filtering does NOT make water safe — prepares for purification.
Step 3: Select Purification Method
Choose by available tools + conditions.
Purification Method Comparison:
┌───────────────┬────────────┬───────────┬────────────┬──────────────────────┐
│ Method │ Kills │ Time │ Requires │ Limitations │
│ │ bacteria/ │ │ │ │
│ │ viruses/ │ │ │ │
│ │ parasites │ │ │ │
├───────────────┼────────────┼───────────┼────────────┼──────────────────────┤
│ Boiling │ Yes/Yes/Yes│ 1-3 min │ Fire, metal│ Fuel, time, does not │
│ │ │ (rolling) │ container │ remove chemicals │
├───────────────┼────────────┼───────────┼────────────┼──────────────────────┤
│ Chlorine │ Yes/Yes/ │ 30 min │ Tablets or │ Less effective in │
│ dioxide tabs │ Yes │ │ drops │ cold/turbid water │
├───────────────┼────────────┼───────────┼────────────┼──────────────────────┤
│ Iodine │ Yes/Yes/ │ 30 min │ Tablets or │ Taste; not for │
│ │ Partial │ │ tincture │ pregnant/thyroid │
│ │ │ │ │ conditions; weak │
│ │ │ │ │ against Crypto │
├───────────────┼────────────┼───────────┼────────────┼──────────────────────┤
│ UV pen │ Yes/Yes/Yes│ 60-90 sec │ UV device, │ Requires clear water;│
│ │ │ per liter │ batteries │ battery dependent │
├───────────────┼────────────┼───────────┼────────────┼──────────────────────┤
│ Pump/squeeze │ Yes/No*/ │ Immediate │ Filter │ Most don't remove │
│ filter │ Yes │ │ device │ viruses (*unless │
│ │ │ │ │ 0.02 micron) │
├───────────────┼────────────┼───────────┼────────────┼──────────────────────┤
│ SODIS (solar) │ Yes/Yes/ │ 6-48 hrs │ Clear PET │ Slow; needs sun; │
│ │ Partial │ │ bottle, │ only 1-2 L at a time │
│ │ │ │ sunlight │ │
└───────────────┴────────────┴───────────┴────────────┴──────────────────────┘
Decision logic:
- Have fire + metal pot? → Boil (most reliable)
- Have chemical tablets? → Chemical treatment
- Have filter + tablet combo? → Filter then treat (belt-and-suspenders)
- Sunny day + clear PET bottles? → SODIS as a backup method
- Multiple methods available? → Use two for maximum safety
→ Clear decision on method(s) based on available tools.
If err: no standard tools → boiling = default, needs only fire + heat-safe container. Even single-wall metal water bottle works. Dire emergency → improvise from rock depression or green bamboo section near flames.
Step 4: Boil Water
Most reliable field method. Kills all pathogen classes.
Boiling Procedure:
1. Bring water to a ROLLING boil (large bubbles breaking the surface)
2. Maintain rolling boil for:
- Sea level to 2000 m / 6500 ft: 1 minute
- 2000-4000 m / 6500-13000 ft: 3 minutes
- Above 4000 m / 13000 ft: 5 minutes
3. Remove from heat
4. Allow to cool in the covered container
5. If taste is flat, pour between two containers several times to aerate
Altitude Adjustment:
Water boils at lower temperatures at altitude.
At 3000 m / 10000 ft, water boils at ~90°C / 194°F.
Longer boiling compensates for the lower temperature.
Fuel Estimate:
Boiling 1 L requires roughly 15-20 min of sustained fire
depending on container, wind, and starting temperature.
→ Vigorous rolling boil maintained for appropriate duration. After cool, safe from biological pathogens.
If err: can't maintain rolling boil (wind, weak fire) → extend time. Container leaks/cracks → transfer to another vessel. No metal container → boil in wooden, bark, or hide container w/ hot rocks: heat stones in fire 20+ min, transfer to water container w/ tongs or sticks. Avoid river rocks (may crack/explode from trapped moisture).
Step 5: Apply Chemical Treatment
When boiling impractical or as secondary treatment.
Chemical Treatment Dosages:
┌─────────────────────┬──────────────────┬────────────┬─────────────────────┐
│ Chemical │ Dose per liter │ Wait time │ Notes │
├─────────────────────┼──────────────────┼────────────┼─────────────────────┤
│ Chlorine dioxide │ Per manufacturer │ 30 min │ Most effective │
│ tablets │ (usually 1 tab │ (4 hrs for │ chemical method; │
│ (e.g., Aquamira, │ per 1 L) │ Crypto) │ kills all pathogens │
│ Katadyn Micropur) │ │ │ │
├─────────────────────┼──────────────────┼────────────┼─────────────────────┤
│ Iodine tablets │ 1-2 tablets per │ 30 min │ Weak against │
│ │ liter │ │ Cryptosporidium │
├─────────────────────┼──────────────────┼────────────┼─────────────────────┤
│ Tincture of iodine │ 5 drops per │ 30 min │ Double dose for │
│ (2%) │ liter (clear) │ (60 min if │ cloudy water │
│ │ 10 drops per │ cold/turbid│ │
│ │ liter (cloudy) │ ) │ │
├─────────────────────┼──────────────────┼────────────┼─────────────────────┤
│ Household bleach │ 2 drops per │ 30 min │ Must be unscented, │
│ (5-8% sodium │ liter (clear) │ │ plain bleach; │
│ hypochlorite) │ 4 drops per │ │ check expiry date │
│ │ liter (cloudy) │ │ │
└─────────────────────┴──────────────────┴────────────┴─────────────────────┘
After treatment, water should have a slight chlorine/iodine smell.
If no smell is detected, add half the original dose and wait another 15 min.
Cold/turbid water adjustment:
- Temperature below 5°C / 40°F: double the wait time
- Turbid water: double the dose OR pre-filter first (recommended)
→ Treated water has faint chemical smell after wait → adequate disinfection. Safe from bacteria + viruses; chlorine dioxide also effective against parasites.
If err: tablets expired (no smell after treatment) → double dose or combine w/ another method. Taste objectionable → stand uncovered 30 min to off-gas, or pour through improvised charcoal filter. Chemical only + suspect Cryptosporidium (livestock) → wait full 4 hrs for chlorine dioxide or combine w/ filtration.
Step 6: Store Safely
Purified water can be recontaminated through dirty containers or hands.
Safe Storage Practices:
1. Store in clean, dedicated containers (do not reuse unpurified containers)
2. If reusing a container, rinse it with a small amount of purified water first
3. Keep containers sealed or covered
4. Mark or separate "raw" and "purified" containers
(e.g., tie a knot in the purified bottle's paracord handle)
5. Avoid reaching into containers with hands — pour, don't dip
6. In warm weather, consume within 24 hours
7. Re-treat water that has been stored more than 24 hours
Hydration Planning:
- Minimum: 2 L / 0.5 gal per day (sedentary, cool weather)
- Active: 4-6 L / 1-1.5 gal per day (hiking, hot weather)
- Plan purification capacity to meet daily needs
→ Purified water safe in clean sealed containers. System avoids cross-contamination.
If err: containers limited → designate one "raw" (collection only), another "clean" (purified only). Scratch/mark distinctly. Suspect recontamination → re-treat before drinking.
Check
- Source assessed + best available picked
- Sediment pre-filtered from turbid water before purification
- Method appropriate for available tools + conditions
- Boiling reached + maintained rolling boil for altitude-adjusted duration
- Chemical treatment correct dosage + wait time
- Purified water stored in clean, sealed, labeled containers
- Sufficient water purified for daily hydration
Traps
- Skip pre-filter: Sediment reduces chemical effectiveness + clogs filters. Always pre-filter turbid.
- Incomplete boiling: Few bubbles on bottom ≠ rolling boil. Wait for vigorous surface-breaking bubbles.
- Ignore altitude: Water boils at lower temps at altitude. Increase boiling time.
- Chemical under-dose: Cold or turbid → more chemical or longer contact time.
- Cross-contamination: Same container for raw + purified, or handling drinking rim w/ dirty hands.
- Single method for worst-case: Stagnant or livestock-adjacent → 2 methods (filter + chemical, or boil + chemical).
→
make-fire— required for boiling; fire also provides warmth while waiting for chemical treatmentforage-plants— some plants indicate nearby water (willows, cattails, cottonwood); foraged food may need clean water for prep