🚨 Critical: Dirty water can cause deadly diseases (cholera, typhus, diarrhea).
Filtering alone is not enough – always disinfect!
1. Why Filter Water?
Even clear water can contain dangerous bacteria, viruses, parasites (e.g. Giardia) and chemicals. In disaster, water supply is often contaminated. A reliable filter is vital.
2. Filter Methods Overview
| Method | Removes | Advantages | Disadvantages |
|---|---|---|---|
| Candle filter (ceramic) | Bacteria, protozoa | Reusable, long-lasting | Not viruses, slow |
| Activated carbon | Chemicals, odor, chlorine | Improves taste | Not germs |
| Membrane filter (0.1µm) | Bacteria, protozoa | Effective, compact | Some viruses not, clogs |
| Improvised filter | Coarse particles | From natural materials | Doesn't remove germs |
| UV light | Bacteria, viruses | No chemicals | Battery/sun needed, turbidity disturbs |
| Boiling | All microorganisms | 100% effective | Energy needed, chemicals remain |
3. The Improvised Water Filter
When no commercial filter is available, build a multi-layer filter:
- Top: Coarse sieve / cloth (removes leaves, insects)
- Layer 1: Coarse gravel / small stones (5-10mm)
- Layer 2: Fine sand (1-2mm) – removes mud
- Layer 3: Activated carbon (from campfire! ground) – removes chemicals
- Layer 4: Fine sand – polishes water
- Layer 5: Cotton/cloth – holds back fine particles
- Outlet: Hole in bottom, collect water
⚠️ The improvised filter removes NO viruses and few bacteria!
Always subsequently boil or treat with chlorine tablets.
4. Disinfect Water
4.1 Boiling (best method)
- Boil water vigorously for 1 minute (3 minutes at altitudes >2000m)
- Leave lid on until water cools (prevents recontamination)
- Kills bacteria, viruses, parasites, eggs
4.2 Chlorine tablets
- 1 tablet per 20-25 liters (depending on manufacturer)
- Let work for 30 minutes
- Chlorine odor is normal – indicates effectiveness
4.3 Bleach solution (emergency)
- Unscented bleach (4-6% sodium hypochlorite)
- 2 drops per liter clear water, 4 drops per liter turbid water
- Let work for 30 minutes
- Slight chlorine odor after 30 min = successful
4.4 SODIS (Solar disinfection)
- Fill clear PET bottles with clear water
- Lay in direct sun for 6 hours (2 days with clouds)
- UV radiation kills microorganisms
- Only for clear water, not turbid!
5. Which Water Sources Are Safe?
| Source | Safety | Measures |
|---|---|---|
| Rainwater (fresh) | Relatively safe | Filter + boiling recommended |
| Spring water | Often safe | Filter, then test |
| River/stream | Risky | Always filter + boil |
| Lake/pond | Risky | Always filter + boil |
| Well (private) | Mostly safe | Regular testing |
| Tap water (blackout) | Varies | Boil if uncertain |
6. Checklist: Water Treatment
- ☐ Candle filter or membrane filter (0.1-0.2µm)
- ☐ Chlorine tablets or bleach solution
- ☐ Cooking option (camping stove, gas, wood)
- ☐ Clear PET bottles for SODIS
- ☐ Coffee filter / clean cloths as pre-filter
- ☐ Activated carbon (for chemicals)
- ☐ pH test strips (optional)