◆ Materials (Required)

Water source — river, stream, pond, rainwater collection, or well
Fire-safe container — metal pot, clay pot, or tin can for boiling
Fire source — wood fire, gas stove, or any heat source
Clear plastic bottles (1-2 liter) — for solar disinfection (SODIS)
Two containers — one for untreated water (DIRTY), one for treated water (CLEAN)
Sand and gravel — for slow sand filtration
Large container with drainage hole — bucket, barrel, or clay pot for filter housing
Cloth — any tightly woven fabric for pre-filtering sediment

◇ Materials (Optional)

Charcoal — crushed, from hardwood fire (improves taste and removes some chemicals)
Lid or cover — for clean water storage (prevents recontamination)
Marking material — to label DIRTY and CLEAN containers clearly

Process

Assess your source — Choose the cleanest available water. Moving water is better than standing water. Upstream is better than downstream. Avoid water near latrines, animal areas, industrial sites, or corpses. Clear water is not safe water — pathogens are invisible.
Pre-filter — Pour water through a cloth folded at least four layers thick. This removes sediment, insects, and large particles. It does NOT make water safe to drink. It is preparation for the next step.
Method 1 — Boiling — Bring water to a full rolling boil. At sea level, one minute of rolling boil kills all common pathogens (bacteria, viruses, protozoa). Above 2000m altitude, boil for three minutes. Cover the container while cooling to prevent recontamination. This is the most reliable single method.
Method 2 — Solar disinfection (SODIS) — Fill clear PET plastic bottles with pre-filtered water. Leave no air bubble. Lay bottles on a dark surface (metal roof, dark cloth) in direct sunlight for minimum 6 hours on a sunny day, or 2 full days under overcast sky. UV radiation kills pathogens. Works only with clear water — if you cannot read text through the bottle, pre-filter more or use another method.
Method 3 — Slow sand filter — Build a filter column: large container with a small drain hole near the bottom, covered with a cloth. Layer from bottom to top: gravel (10cm), coarse sand (10cm), fine sand (40cm). Pour untreated water on top. Collect filtered water from the drain. The first 10 liters flush the filter — discard them. After 2-3 weeks, a biological layer (schmutzdecke) forms on top that actively consumes pathogens. Do not let the filter dry out.
Store safely — Pour treated water into a CLEAN container with a lid. Never dip hands or cups into the clean container — pour only. Label the container. If the storage container was ever used for untreated water, it is contaminated — clean it with boiling water first.
Maintain the chain — Safe water is a chain, not a single step. Source → pre-filter → treat → store clean. If any link breaks, start over. If someone dips a cup into the clean container, re-treat. If the storage container has slime or odor, re-treat and clean the container.

▶ Output

Safe drinking water from any freshwater source, using zero electricity and zero purchased chemicals.

Ceramic filter elements (if available) dramatically increase filtration speed and reliability. Chlorine tablets are effective but create supply dependency.

Unsafe water causes diarrhea, cholera, typhoid, and dysentery. In a crisis, waterborne disease kills more people than the crisis itself.

✓ Verify (No Instruments)

Boiling — You saw a full rolling boil for the required duration. Not simmering, not steaming — a vigorous, continuous boil with large bubbles.
SODIS — Bottles were in direct sunlight for the full required time. Water was clear before filling. Bottles were clear PET plastic, not colored or glass.
Sand filter — Water runs clear from the drain. No sediment visible. Filter has been running for at least 2-3 weeks (biological layer active). Filter never dried out.
Storage — Clean container has no odor, no slime, no sediment. Lid is secure. No one has dipped anything into it.
Health — No increase in diarrhea, vomiting, or stomach illness in the group using the treated water. If symptoms appear, audit every step of the chain.

↻ Common Failures & Recovery

Water still makes people sick — Audit the full chain. The most common failure is recontamination during storage. Check: is the clean container truly clean? Is anyone dipping cups? Is the lid secure?
Cannot reach boiling — Increase airflow to fire. Use dry hardwood. Build a windbreak. Use a smaller container with less water — heat less mass at a time.
SODIS bottles are cloudy — The water was not clear enough. Pre-filter more aggressively. If bottles themselves are cloudy or scratched, replace them. UV cannot penetrate cloudy plastic.
Sand filter runs too slowly — The fine sand layer is too thick or too compacted. Rebuild with slightly coarser sand in the middle layer. Never compress the sand — let it settle naturally.
Sand filter water tastes earthy — Normal for the first weeks. Adding a charcoal layer between the gravel and coarse sand improves taste. Use hardwood charcoal, crushed to gravel-sized pieces.
No fuel for boiling — Switch to SODIS if sunlight is available. Build a sand filter for ongoing supply. Boiling is the gold standard but not the only option.

⚠ Hazards

Steam burns from boiling — Use long tongs or sticks to handle hot containers. Keep face and hands away from the steam. Let water cool before transferring.
False confidence — Clear water is not safe water. Pathogens are invisible. Treat ALL water from natural sources, even if it looks clean.
Filter breakthrough — A damaged sand filter (cracked container, disturbed sand layers, dried-out biological layer) passes untreated water. If the filter was disturbed, discard the first 20 liters after repair and re-establish the biological layer.
Chemical contamination — Boiling, SODIS, and sand filtration remove biological pathogens. They do NOT remove heavy metals, pesticides, or industrial chemicals. If the source is near industrial activity, find a different source.

↔ See also — related cards

I Making Fire From What You Find

Print Verify Index